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path: root/core/includes/form.inc
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<?php

/**
 * @file
 * Functions for form and batch generation and processing.
 */

use Drupal\Component\Utility\Crypt;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Form\FormInterface;
use Drupal\Core\Form\BaseFormIdInterface;
use Drupal\Core\Database\Database;
use Drupal\Core\Template\Attribute;
use Drupal\Core\Datetime\DrupalDateTime;
use Drupal\Core\Utility\Color;

/**
 * @defgroup forms Form builder functions
 * @{
 * Functions that build an abstract representation of a HTML form.
 *
 * All modules should declare their form builder functions to be in this
 * group and each builder function should reference its validate and submit
 * functions using \@see. Conversely, validate and submit functions should
 * reference the form builder function using \@see. For examples, of this see
 * system_modules_uninstall() or user_pass(), the latter of which has the
 * following in its doxygen documentation:
 *
 * \@ingroup forms
 * \@see user_pass_validate().
 * \@see user_pass_submit().
 *
 * @} End of "defgroup forms".
 */

/**
 * @defgroup form_api Form generation
 * @{
 * Functions to enable the processing and display of HTML forms.
 *
 * Drupal uses these functions to achieve consistency in its form processing and
 * presentation, while simplifying code and reducing the amount of HTML that
 * must be explicitly generated by modules.
 *
 * The primary function used with forms is drupal_get_form(), which is
 * used for forms presented interactively to a user. Forms can also be built and
 * submitted programmatically without any user input using the
 * drupal_form_submit() function.
 *
 * drupal_get_form() handles retrieving, processing, and displaying a rendered
 * HTML form for modules automatically.
 *
 * Here is an example of how to use drupal_get_form() and a form builder
 * function:
 * @code
 * $form = drupal_get_form('my_module_example_form');
 * ...
 * function my_module_example_form($form, &$form_state) {
 *   $form['submit'] = array(
 *     '#type' => 'submit',
 *     '#value' => t('Submit'),
 *   );
 *   return $form;
 * }
 * function my_module_example_form_validate($form, &$form_state) {
 *   // Validation logic.
 * }
 * function my_module_example_form_submit($form, &$form_state) {
 *   // Submission logic.
 * }
 * @endcode
 *
 * Or with any number of additional arguments:
 * @code
 * $extra = "extra";
 * $form = drupal_get_form('my_module_example_form', $extra);
 * ...
 * function my_module_example_form($form, &$form_state, $extra) {
 *   $form['submit'] = array(
 *     '#type' => 'submit',
 *     '#value' => $extra,
 *   );
 *   return $form;
 * }
 * @endcode
 *
 * The $form argument to form-related functions is a structured array containing
 * the elements and properties of the form. For information on the array
 * components and format, and more detailed explanations of the Form API
 * workflow, see the
 * @link forms_api_reference.html Form API reference @endlink
 * and the
 * @link http://drupal.org/node/37775 Form API documentation section. @endlink
 * In addition, there is a set of Form API tutorials in
 * @link form_example_tutorial.inc the Form Example Tutorial @endlink which
 * provide basics all the way up through multistep forms.
 *
 * In the form builder, validation, submission, and other form functions,
 * $form_state is the primary influence on the processing of the form and is
 * passed by reference to most functions, so they use it to communicate with
 * the form system and each other.
 *
 * See drupal_build_form() for documentation of $form_state keys.
 */

/**
 * Determines the form ID.
 *
 * @param \Drupal\Core\Form\FormInterface|string $form_arg
 *   A form object to use to build the form, or the unique string identifying
 *   the desired form. If $form_arg is a string and a function with that
 *   name exists, it is called to build the form array.
 * @param array $form_state
 *   An associative array containing the current state of the form.
 *
 * @return string
 *   The unique string identifying the desired form.
 */
function _drupal_form_id($form_arg, &$form_state) {
  // If the $form_arg implements \Drupal\Core\Form\FormInterface, add that as
  // the callback object and determine the form ID.
  if (is_object($form_arg) && $form_arg instanceof FormInterface) {
    $form_state['build_info']['callback_object'] = $form_arg;
    if ($form_arg instanceof BaseFormIdInterface) {
      $form_state['build_info']['base_form_id'] = $form_arg->getBaseFormID();
    }
    return $form_arg->getFormID();
  }

  // Otherwise, the $form_arg is the form ID.
  return $form_arg;
}

/**
 * Returns a renderable form array for a given form ID.
 *
 * This function should be used instead of drupal_build_form() when $form_state
 * is not needed (i.e., when initially rendering the form) and is often
 * used as a menu callback.
 *
 * @param \Drupal\Core\Form\FormInterface|string $form_arg
 *   A form object to use to build the form, or the unique string identifying
 *   the desired form. If $form_arg is a string and a function with that
 *   name exists, it is called to build the form array. Modules that need to
 *   generate the same form (or very similar forms) using different $form_ids
 *   can implement hook_forms(), which maps different $form_id values to the
 *   proper form constructor function. Examples may be found in node_forms(),
 *   and search_forms().
 * @param ...
 *   Any additional arguments are passed on to the functions called by
 *   drupal_get_form(), including the unique form constructor function. For
 *   example, the node_edit form requires that a node object is passed in here
 *   when it is called. These are available to implementations of
 *   hook_form_alter() and hook_form_FORM_ID_alter() as the array
 *   $form_state['build_info']['args'].
 *
 * @return
 *   The form array.
 *
 * @see drupal_build_form()
 */
function drupal_get_form($form_arg) {
  $form_state = array();

  $args = func_get_args();
  // Remove $form_arg from the arguments.
  array_shift($args);
  $form_state['build_info']['args'] = $args;

  $form_id = _drupal_form_id($form_arg, $form_state);
  return drupal_build_form($form_id, $form_state);
}

/**
 * Builds and processes a form for a given form ID.
 *
 * The form may also be retrieved from the cache if the form was built in a
 * previous page-load. The form is then passed on for processing, validation
 * and submission if there is proper input.
 *
 * @param $form_id
 *   The unique string identifying the desired form. If a function with that
 *   name exists, it is called to build the form array. Modules that need to
 *   generate the same form (or very similar forms) using different $form_ids
 *   can implement hook_forms(), which maps different $form_id values to the
 *   proper form constructor function. Examples may be found in node_forms(),
 *   and search_forms().
 * @param $form_state
 *   An array which stores information about the form. This is passed as a
 *   reference so that the caller can use it to examine what in the form changed
 *   when the form submission process is complete. Furthermore, it may be used
 *   to store information related to the processed data in the form, which will
 *   persist across page requests when the 'cache' or 'rebuild' flag is set.
 *   The following parameters may be set in $form_state to affect how the form
 *   is rendered:
 *   - build_info: Internal. An associative array of information stored by Form
 *     API that is necessary to build and rebuild the form from cache when the
 *     original context may no longer be available:
 *     - callback: The actual callback to be used to retrieve the form array. If
 *       none is provided $form_id is used instead. Can be any callable type.
 *     - args: A list of arguments to pass to the form constructor.
 *     - files: An optional array defining include files that need to be loaded
 *       for building the form. Each array entry may be the path to a file or
 *       another array containing values for the parameters 'type', 'module' and
 *       'name' as needed by module_load_include(). The files listed here are
 *       automatically loaded by form_get_cache(). By default the current menu
 *       router item's 'file' definition is added, if any. Use
 *       form_load_include() to add include files from a form constructor.
 *     - form_id: Identification of the primary form being constructed and
 *       processed.
 *     - base_form_id: Identification for a base form, as declared in a
 *       hook_forms() implementation.
 *   - rebuild_info: Internal. Similar to 'build_info', but pertaining to
 *     drupal_rebuild_form().
 *   - rebuild: Normally, after the entire form processing is completed and
 *     submit handlers have run, a form is considered to be done and
 *     drupal_redirect_form() will redirect the user to a new page using a GET
 *     request (so a browser refresh does not re-submit the form). However, if
 *     'rebuild' has been set to TRUE, then a new copy of the form is
 *     immediately built and sent to the browser, instead of a redirect. This is
 *     used for multi-step forms, such as wizards and confirmation forms.
 *     Normally, $form_state['rebuild'] is set by a submit handler, since it is
 *     usually logic within a submit handler that determines whether a form is
 *     done or requires another step. However, a validation handler may already
 *     set $form_state['rebuild'] to cause the form processing to bypass submit
 *     handlers and rebuild the form instead, even if there are no validation
 *     errors.
 *   - redirect: Used to redirect the form on submission. It may either be a
 *     string containing the destination URL, or an array of arguments
 *     compatible with drupal_goto(). See drupal_redirect_form() for complete
 *     information.
 *   - no_redirect: If set to TRUE the form will NOT perform a drupal_goto(),
 *     even if 'redirect' is set.
 *   - method: The HTTP form method to use for finding the input for this form.
 *     May be 'post' or 'get'. Defaults to 'post'. Note that 'get' method
 *     forms do not use form ids so are always considered to be submitted, which
 *     can have unexpected effects. The 'get' method should only be used on
 *     forms that do not change data, as that is exclusively the domain of
 *     'post.'
 *   - cache: If set to TRUE the original, unprocessed form structure will be
 *     cached, which allows the entire form to be rebuilt from cache. A typical
 *     form workflow involves two page requests; first, a form is built and
 *     rendered for the user to fill in. Then, the user fills the form in and
 *     submits it, triggering a second page request in which the form must be
 *     built and processed. By default, $form and $form_state are built from
 *     scratch during each of these page requests. Often, it is necessary or
 *     desired to persist the $form and $form_state variables from the initial
 *     page request to the one that processes the submission. 'cache' can be set
 *     to TRUE to do this. A prominent example is an Ajax-enabled form, in which
 *     ajax_process_form() enables form caching for all forms that include an
 *     element with the #ajax property. (The Ajax handler has no way to build
 *     the form itself, so must rely on the cached version.) Note that the
 *     persistence of $form and $form_state happens automatically for
 *     (multi-step) forms having the 'rebuild' flag set, regardless of the value
 *     for 'cache'.
 *   - no_cache: If set to TRUE the form will NOT be cached, even if 'cache' is
 *     set.
 *   - values: An associative array of values submitted to the form. The
 *     validation functions and submit functions use this array for nearly all
 *     their decision making. (Note that #tree determines whether the values
 *     are a flat array or an array whose structure parallels the $form array.
 *     See the @link forms_api_reference.html Form API reference @endlink for
 *     more information.)
 *   - input: The array of values as they were submitted by the user. These are
 *     raw and unvalidated, so should not be used without a thorough
 *     understanding of security implications. In almost all cases, code should
 *     use the data in the 'values' array exclusively. The most common use of
 *     this key is for multi-step forms that need to clear some of the user
 *     input when setting 'rebuild'. The values correspond to $_POST or $_GET,
 *     depending on the 'method' chosen.
 *   - always_process: If TRUE and the method is GET, a form_id is not
 *     necessary. This should only be used on RESTful GET forms that do NOT
 *     write data, as this could lead to security issues. It is useful so that
 *     searches do not need to have a form_id in their query arguments to
 *     trigger the search.
 *   - must_validate: Ordinarily, a form is only validated once, but there are
 *     times when a form is resubmitted internally and should be validated
 *     again. Setting this to TRUE will force that to happen. This is most
 *     likely to occur during Ajax operations.
 *   - programmed: If TRUE, the form was submitted programmatically, usually
 *     invoked via drupal_form_submit(). Defaults to FALSE.
 *   - process_input: Boolean flag. TRUE signifies correct form submission.
 *     This is always TRUE for programmed forms coming from drupal_form_submit()
 *     (see 'programmed' key), or if the form_id coming from the $_POST data is
 *     set and matches the current form_id.
 *   - submitted: If TRUE, the form has been submitted. Defaults to FALSE.
 *   - executed: If TRUE, the form was submitted and has been processed and
 *     executed. Defaults to FALSE.
 *   - triggering_element: (read-only) The form element that triggered
 *     submission, which may or may not be a button (in the case of Ajax forms).
 *     This key is often used to distinguish between various buttons in a submit
 *     handler, and is also used in Ajax handlers.
 *   - has_file_element: Internal. If TRUE, there is a file element and Form API
 *     will set the appropriate 'enctype' HTML attribute on the form.
 *   - groups: Internal. An array containing references to details elements to
 *     render them within vertical tabs.
 *   - storage: $form_state['storage'] is not a special key, and no specific
 *     support is provided for it in the Form API. By tradition it was
 *     the location where application-specific data was stored for communication
 *     between the submit, validation, and form builder functions, especially
 *     in a multi-step-style form. Form implementations may use any key(s)
 *     within $form_state (other than the keys listed here and other reserved
 *     ones used by Form API internals) for this kind of storage. The
 *     recommended way to ensure that the chosen key doesn't conflict with ones
 *     used by the Form API or other modules is to use the module name as the
 *     key name or a prefix for the key name. For example, the entity form
 *     controller classes use $this->entity in entity forms, or
 *     $form_state['controller']->getEntity() outside the controller, to store
 *     information about the entity being edited, and this information stays
 *     available across successive clicks of the "Preview" button (if available)
 *     as well as when the "Save" button is finally clicked.
 *   - buttons: A list containing copies of all submit and button elements in
 *     the form.
 *   - complete_form: A reference to the $form variable containing the complete
 *     form structure. #process, #after_build, #element_validate, and other
 *     handlers being invoked on a form element may use this reference to access
 *     other information in the form the element is contained in.
 *   - temporary: An array holding temporary data accessible during the current
 *     page request only. All $form_state properties that are not reserved keys
 *     (see form_state_keys_no_cache()) persist throughout a multistep form
 *     sequence. Form API provides this key for modules to communicate
 *     information across form-related functions during a single page request.
 *     It may be used to temporarily save data that does not need to or should
 *     not be cached during the whole form workflow; e.g., data that needs to be
 *     accessed during the current form build process only. There is no use-case
 *     for this functionality in Drupal core.
 *   - wrapper_callback: Modules that wish to pre-populate certain forms with
 *     common elements, such as back/next/save buttons in multi-step form
 *     wizards, may define a form builder function name that returns a form
 *     structure, which is passed on to the actual form builder function.
 *     Such implementations may either define the 'wrapper_callback' via
 *     hook_forms() or have to invoke drupal_build_form() (instead of
 *     drupal_get_form()) on their own in a custom menu callback to prepare
 *     $form_state accordingly.
 *   Information on how certain $form_state properties control redirection
 *   behavior after form submission may be found in drupal_redirect_form().
 *
 * @return
 *   The rendered form. This function may also perform a redirect and hence may
 *   not return at all, depending upon the $form_state flags that were set.
 *
 * @see drupal_redirect_form()
 */
function drupal_build_form($form_id, &$form_state) {
  // Ensure some defaults; if already set they will not be overridden.
  $form_state += form_state_defaults();

  if (!isset($form_state['input'])) {
    $form_state['input'] = $form_state['method'] == 'get' ? $_GET : $_POST;
  }

  if (isset($_SESSION['batch_form_state'])) {
    // We've been redirected here after a batch processing. The form has
    // already been processed, but needs to be rebuilt. See _batch_finished().
    $form_state = $_SESSION['batch_form_state'];
    unset($_SESSION['batch_form_state']);
    return drupal_rebuild_form($form_id, $form_state);
  }

  // If the incoming input contains a form_build_id, we'll check the cache for a
  // copy of the form in question. If it's there, we don't have to rebuild the
  // form to proceed. In addition, if there is stored form_state data from a
  // previous step, we'll retrieve it so it can be passed on to the form
  // processing code.
  $check_cache = isset($form_state['input']['form_id']) && $form_state['input']['form_id'] == $form_id && !empty($form_state['input']['form_build_id']);
  if ($check_cache) {
    $form = form_get_cache($form_state['input']['form_build_id'], $form_state);
  }

  // If the previous bit of code didn't result in a populated $form object, we
  // are hitting the form for the first time and we need to build it from
  // scratch.
  if (!isset($form)) {
    // If we attempted to serve the form from cache, uncacheable $form_state
    // keys need to be removed after retrieving and preparing the form, except
    // any that were already set prior to retrieving the form.
    if ($check_cache) {
      $form_state_before_retrieval = $form_state;
    }

    $form = drupal_retrieve_form($form_id, $form_state);
    drupal_prepare_form($form_id, $form, $form_state);

    // form_set_cache() removes uncacheable $form_state keys defined in
    // form_state_keys_no_cache() in order for multi-step forms to work
    // properly. This means that form processing logic for single-step forms
    // using $form_state['cache'] may depend on data stored in those keys
    // during drupal_retrieve_form()/drupal_prepare_form(), but form
    // processing should not depend on whether the form is cached or not, so
    // $form_state is adjusted to match what it would be after a
    // form_set_cache()/form_get_cache() sequence. These exceptions are
    // allowed to survive here:
    // - always_process: Does not make sense in conjunction with form caching
    //   in the first place, since passing form_build_id as a GET parameter is
    //   not desired.
    // - temporary: Any assigned data is expected to survives within the same
    //   page request.
    if ($check_cache) {
      $uncacheable_keys = array_flip(array_diff(form_state_keys_no_cache(), array('always_process', 'temporary')));
      $form_state = array_diff_key($form_state, $uncacheable_keys);
      $form_state += $form_state_before_retrieval;
    }
  }

  // Now that we have a constructed form, process it. This is where:
  // - Element #process functions get called to further refine $form.
  // - User input, if any, gets incorporated in the #value property of the
  //   corresponding elements and into $form_state['values'].
  // - Validation and submission handlers are called.
  // - If this submission is part of a multistep workflow, the form is rebuilt
  //   to contain the information of the next step.
  // - If necessary, the form and form state are cached or re-cached, so that
  //   appropriate information persists to the next page request.
  // All of the handlers in the pipeline receive $form_state by reference and
  // can use it to know or update information about the state of the form.
  drupal_process_form($form_id, $form, $form_state);

  // If this was a successful submission of a single-step form or the last step
  // of a multi-step form, then drupal_process_form() issued a redirect to
  // another page, or back to this page, but as a new request. Therefore, if
  // we're here, it means that this is either a form being viewed initially
  // before any user input, or there was a validation error requiring the form
  // to be re-displayed, or we're in a multi-step workflow and need to display
  // the form's next step. In any case, we have what we need in $form, and can
  // return it for rendering.
  return $form;
}

/**
 * Retrieves default values for the $form_state array.
 */
function form_state_defaults() {
  return array(
    'rebuild' => FALSE,
    'rebuild_info' => array(),
    'redirect' => NULL,
    // @todo 'args' is usually set, so no other default 'build_info' keys are
    //   appended via += form_state_defaults().
    'build_info' => array(
      'args' => array(),
      'files' => array(),
    ),
    'temporary' => array(),
    'submitted' => FALSE,
    'executed' => FALSE,
    'programmed' => FALSE,
    'cache'=> FALSE,
    'method' => 'post',
    'groups' => array(),
    'buttons' => array(),
  );
}

/**
 * Constructs a new $form from the information in $form_state.
 *
 * This is the key function for making multi-step forms advance from step to
 * step. It is called by drupal_process_form() when all user input processing,
 * including calling validation and submission handlers, for the request is
 * finished. If a validate or submit handler set $form_state['rebuild'] to TRUE,
 * and if other conditions don't preempt a rebuild from happening, then this
 * function is called to generate a new $form, the next step in the form
 * workflow, to be returned for rendering.
 *
 * Ajax form submissions are almost always multi-step workflows, so that is one
 * common use-case during which form rebuilding occurs. See ajax_form_callback()
 * for more information about creating Ajax-enabled forms.
 *
 * @param $form_id
 *   The unique string identifying the desired form. If a function
 *   with that name exists, it is called to build the form array.
 *   Modules that need to generate the same form (or very similar forms)
 *   using different $form_ids can implement hook_forms(), which maps
 *   different $form_id values to the proper form constructor function. Examples
 *   may be found in node_forms() and search_forms().
 * @param $form_state
 *   A keyed array containing the current state of the form.
 * @param $old_form
 *   (optional) A previously built $form. Used to retain the #build_id and
 *   #action properties in Ajax callbacks and similar partial form rebuilds. The
 *   only properties copied from $old_form are the ones which both exist in
 *   $old_form and for which $form_state['rebuild_info']['copy'][PROPERTY] is
 *   TRUE. If $old_form is not passed, the entire $form is rebuilt freshly.
 *   'rebuild_info' needs to be a separate top-level property next to
 *   'build_info', since the contained data must not be cached.
 *
 * @return
 *   The newly built form.
 *
 * @see drupal_process_form()
 * @see ajax_form_callback()
 */
function drupal_rebuild_form($form_id, &$form_state, $old_form = NULL) {
  $form = drupal_retrieve_form($form_id, $form_state);

  // If only parts of the form will be returned to the browser (e.g., Ajax or
  // RIA clients), re-use the old #build_id to not require client-side code to
  // manually update the hidden 'build_id' input element.
  // Otherwise, a new #build_id is generated, to not clobber the previous
  // build's data in the form cache; also allowing the user to go back to an
  // earlier build, make changes, and re-submit.
  // @see drupal_prepare_form()
  if (isset($old_form['#build_id']) && !empty($form_state['rebuild_info']['copy']['#build_id'])) {
    $form['#build_id'] = $old_form['#build_id'];
  }
  else {
    $form['#build_id'] = 'form-' . Crypt::hashBase64(uniqid(mt_rand(), TRUE) . mt_rand());
  }

  // #action defaults to request_uri(), but in case of Ajax and other partial
  // rebuilds, the form is submitted to an alternate URL, and the original
  // #action needs to be retained.
  if (isset($old_form['#action']) && !empty($form_state['rebuild_info']['copy']['#action'])) {
    $form['#action'] = $old_form['#action'];
  }

  drupal_prepare_form($form_id, $form, $form_state);

  // Caching is normally done in drupal_process_form(), but what needs to be
  // cached is the $form structure before it passes through form_builder(),
  // so we need to do it here.
  // @todo For Drupal 8, find a way to avoid this code duplication.
  if (empty($form_state['no_cache'])) {
    form_set_cache($form['#build_id'], $form, $form_state);
  }

  // Clear out all group associations as these might be different when
  // re-rendering the form.
  $form_state['groups'] = array();

  // Return a fully built form that is ready for rendering.
  return form_builder($form_id, $form, $form_state);
}

/**
 * Fetches a form from the cache.
 */
function form_get_cache($form_build_id, &$form_state) {
  if ($form = Drupal::keyValueExpirable('form')->get($form_build_id)) {
    global $user;
    if ((isset($form['#cache_token']) && drupal_valid_token($form['#cache_token'])) || (!isset($form['#cache_token']) && !$user->uid)) {
      if ($stored_form_state = Drupal::keyValueExpirable('form_state')->get($form_build_id)) {
        // Re-populate $form_state for subsequent rebuilds.
        $form_state = $stored_form_state + $form_state;

        // If the original form is contained in include files, load the files.
        // @see form_load_include()
        $form_state['build_info'] += array('files' => array());
        foreach ($form_state['build_info']['files'] as $file) {
          if (is_array($file)) {
            $file += array('type' => 'inc', 'name' => $file['module']);
            module_load_include($file['type'], $file['module'], $file['name']);
          }
          elseif (file_exists($file)) {
            require_once DRUPAL_ROOT . '/' . $file;
          }
        }
      }
      return $form;
    }
  }
}

/**
 * Stores a form in the cache.
 */
function form_set_cache($form_build_id, $form, $form_state) {
  // 6 hours cache life time for forms should be plenty.
  $expire = 21600;

  // Cache form structure.
  if (isset($form)) {
    if ($GLOBALS['user']->uid) {
      $form['#cache_token'] = drupal_get_token();
    }
    Drupal::keyValueExpirable('form')->setWithExpire($form_build_id, $form, $expire);
  }

  // Cache form state.
  if ($data = array_diff_key($form_state, array_flip(form_state_keys_no_cache()))) {
    Drupal::keyValueExpirable('form_state')->setWithExpire($form_build_id, $data, $expire);
  }
}

/**
 * Returns an array of $form_state keys that shouldn't be cached.
 */
function form_state_keys_no_cache() {
  return array(
    // Public properties defined by form constructors and form handlers.
    'always_process',
    'must_validate',
    'rebuild',
    'rebuild_info',
    'redirect',
    'no_redirect',
    'temporary',
    // Internal properties defined by form processing.
    'buttons',
    'triggering_element',
    'complete_form',
    'groups',
    'input',
    'method',
    'submit_handlers',
    'submitted',
    'executed',
    'validate_handlers',
    'values',
  );
}

/**
 * Ensures an include file is loaded whenever the form is processed.
 *
 * Example:
 * @code
 *   // Load node.admin.inc from Node module.
 *   form_load_include($form_state, 'inc', 'node', 'node.admin');
 * @endcode
 *
 * Use this function instead of module_load_include() from inside a form
 * constructor or any form processing logic as it ensures that the include file
 * is loaded whenever the form is processed. In contrast to using
 * module_load_include() directly, form_load_include() makes sure the include
 * file is correctly loaded also if the form is cached.
 *
 * @param $form_state
 *   The current state of the form.
 * @param $type
 *   The include file's type (file extension).
 * @param $module
 *   The module to which the include file belongs.
 * @param $name
 *   (optional) The base file name (without the $type extension). If omitted,
 *   $module is used; i.e., resulting in "$module.$type" by default.
 *
 * @return
 *   The filepath of the loaded include file, or FALSE if the include file was
 *   not found or has been loaded already.
 *
 * @see module_load_include()
 */
function form_load_include(&$form_state, $type, $module, $name = NULL) {
  if (!isset($name)) {
    $name = $module;
  }
  if (!isset($form_state['build_info']['files']["$module:$name.$type"])) {
    // Only add successfully included files to the form state.
    if ($result = module_load_include($type, $module, $name)) {
      $form_state['build_info']['files']["$module:$name.$type"] = array(
        'type' => $type,
        'module' => $module,
        'name' => $name,
      );
      return $result;
    }
  }
  return FALSE;
}

/**
 * Retrieves, populates, and processes a form.
 *
 * This function allows you to supply values for form elements and submit a
 * form for processing. Compare to drupal_get_form(), which also builds and
 * processes a form, but does not allow you to supply values.
 *
 * There is no return value, but you can check to see if there are errors
 * by calling form_get_errors().
 *
 * @param \Drupal\Core\Form\FormInterface|string $form_arg
 *   A form object to use to build the form, or the unique string identifying
 *   the desired form. If $form_arg is a string and a function with that
 *   name exists, it is called to build the form array. Modules that need to
 *   generate the same form (or very similar forms) using different $form_ids
 *   can implement hook_forms(), which maps different $form_id values to the
 *   proper form constructor function. Examples may be found in node_forms()
 *   and search_forms().
 * @param $form_state
 *   A keyed array containing the current state of the form. Most important is
 *   the $form_state['values'] collection, a tree of data used to simulate the
 *   incoming $_POST information from a user's form submission. If a key is not
 *   filled in $form_state['values'], then the default value of the respective
 *   element is used. To submit an unchecked checkbox or other control that
 *   browsers submit by not having a $_POST entry, include the key, but set the
 *   value to NULL.
 * @param ...
 *   Any additional arguments are passed on to the functions called by
 *   drupal_form_submit(), including the unique form constructor function.
 *   For example, the node_edit form requires that a node object be passed
 *   in here when it is called. Arguments that need to be passed by reference
 *   should not be included here, but rather placed directly in the $form_state
 *   build info array so that the reference can be preserved. For example, a
 *   form builder function with the following signature:
 *   @code
 *   function mymodule_form($form, &$form_state, &$object) {
 *   }
 *   @endcode
 *   would be called via drupal_form_submit() as follows:
 *   @code
 *   $form_state['values'] = $my_form_values;
 *   $form_state['build_info']['args'] = array(&$object);
 *   drupal_form_submit('mymodule_form', $form_state);
 *   @endcode
 * For example:
 * @code
 * // register a new user
 * $form_state = array();
 * $form_state['values']['name'] = 'robo-user';
 * $form_state['values']['mail'] = 'robouser@example.com';
 * $form_state['values']['pass']['pass1'] = 'password';
 * $form_state['values']['pass']['pass2'] = 'password';
 * $form_state['values']['op'] = t('Create new account');
 * drupal_form_submit('user_register_form', $form_state);
 * @endcode
 */
function drupal_form_submit($form_arg, &$form_state) {
  if (!isset($form_state['build_info']['args'])) {
    $args = func_get_args();
    array_shift($args);
    array_shift($args);
    $form_state['build_info']['args'] = $args;
  }
  // Merge in default values.
  $form_state += form_state_defaults();

  // Populate $form_state['input'] with the submitted values before retrieving
  // the form, to be consistent with what drupal_build_form() does for
  // non-programmatic submissions (form builder functions may expect it to be
  // there).
  $form_state['input'] = $form_state['values'];

  $form_state['programmed'] = TRUE;

  $form_id = _drupal_form_id($form_arg, $form_state);
  $form = drupal_retrieve_form($form_id, $form_state);
  // Programmed forms are always submitted.
  $form_state['submitted'] = TRUE;

  // Reset form validation.
  $form_state['must_validate'] = TRUE;
  form_clear_error();

  drupal_prepare_form($form_id, $form, $form_state);
  drupal_process_form($form_id, $form, $form_state);
}

/**
 * Retrieves the structured array that defines a given form.
 *
 * @param $form_id
 *   The unique string identifying the desired form. If a function
 *   with that name exists, it is called to build the form array.
 *   Modules that need to generate the same form (or very similar forms)
 *   using different $form_ids can implement hook_forms(), which maps
 *   different $form_id values to the proper form constructor function.
 * @param $form_state
 *   A keyed array containing the current state of the form, including the
 *   additional arguments to drupal_get_form() or drupal_form_submit() in the
 *   'args' component of the array.
 */
function drupal_retrieve_form($form_id, &$form_state) {
  $forms = &drupal_static(__FUNCTION__);

  // Record the $form_id.
  $form_state['build_info']['form_id'] = $form_id;

  // Record the filepath of the include file containing the original form, so
  // the form builder callbacks can be loaded when the form is being rebuilt
  // from cache on a different path (such as 'system/ajax'). See
  // form_get_cache(). Don't do this in maintenance mode as Drupal may not be
  // fully bootstrapped (i.e. during installation) in which case
  // menu_get_item() is not available.
  if (!isset($form_state['build_info']['files']['menu']) && !defined('MAINTENANCE_MODE')) {
    $item = menu_get_item();
    if (!empty($item['include_file'])) {
      // Do not use form_load_include() here, as the file is already loaded.
      // Anyway, form_get_cache() is able to handle filepaths too.
      $form_state['build_info']['files']['menu'] = $item['include_file'];
    }
  }

  // We save two copies of the incoming arguments: one for modules to use
  // when mapping form ids to constructor functions, and another to pass to
  // the constructor function itself.
  $args = $form_state['build_info']['args'];

  // If an explicit form builder callback is defined we just use it, otherwise
  // we look for a function named after the $form_id.
  $callback = $form_id;
  if (!empty($form_state['build_info']['callback'])) {
    $callback = $form_state['build_info']['callback'];
  }
  elseif (!empty($form_state['build_info']['callback_object'])) {
    $callback = array($form_state['build_info']['callback_object'], 'buildForm');
  }

  // We first check to see if there is a valid form builder callback defined.
  // If there is, we simply pass the arguments on to it to get the form.
  if (!is_callable($callback)) {
    // In cases where many form_ids need to share a central constructor function,
    // such as the node editing form, modules can implement hook_forms(). It
    // maps one or more form_ids to the correct constructor functions.
    //
    // We cache the results of that hook to save time, but that only works
    // for modules that know all their form_ids in advance. (A module that
    // adds a small 'rate this comment' form to each comment in a list
    // would need a unique form_id for each one, for example.)
    //
    // So, we call the hook if $forms isn't yet populated, OR if it doesn't
    // yet have an entry for the requested form_id.
    if (!isset($forms) || !isset($forms[$form_id])) {
      $forms = module_invoke_all('forms', $form_id, $args);
    }
    $form_definition = $forms[$form_id];
    if (isset($form_definition['callback arguments'])) {
      $args = array_merge($form_definition['callback arguments'], $args);
    }
    if (isset($form_definition['callback'])) {
      $callback = $form_definition['callback'];
      $form_state['build_info']['base_form_id'] = $callback;
    }
    // In case $form_state['wrapper_callback'] is not defined already, we also
    // allow hook_forms() to define one.
    if (!isset($form_state['wrapper_callback']) && isset($form_definition['wrapper_callback'])) {
      $form_state['wrapper_callback'] = $form_definition['wrapper_callback'];
    }
  }

  $form = array();
  // Assign a default CSS class name based on $form_id.
  // This happens here and not in drupal_prepare_form() in order to allow the
  // form constructor function to override or remove the default class.
  $form['#attributes']['class'][] = drupal_html_class($form_id);
  // Same for the base form ID, if any.
  if (isset($form_state['build_info']['base_form_id'])) {
    $form['#attributes']['class'][] = drupal_html_class($form_state['build_info']['base_form_id']);
  }

  // We need to pass $form_state by reference in order for forms to modify it,
  // since call_user_func_array() requires that referenced variables are passed
  // explicitly.
  $args = array_merge(array($form, &$form_state), $args);

  // When the passed $form_state (not using drupal_get_form()) defines a
  // 'wrapper_callback', then it requests to invoke a separate (wrapping) form
  // builder function to pre-populate the $form array with form elements, which
  // the actual form builder function ($callback) expects. This allows for
  // pre-populating a form with common elements for certain forms, such as
  // back/next/save buttons in multi-step form wizards. See drupal_build_form().
  if (isset($form_state['wrapper_callback'])) {
    $form = call_user_func_array($form_state['wrapper_callback'], $args);
    // Put the prepopulated $form into $args.
    $args[0] = $form;
  }

  // If $callback was returned by a hook_forms() implementation, call it.
  // Otherwise, call the function named after the form id.
  $form = call_user_func_array($callback, $args);
  $form['#form_id'] = $form_id;

  return $form;
}

/**
 * Processes a form submission.
 *
 * This function is the heart of form API. The form gets built, validated and in
 * appropriate cases, submitted and rebuilt.
 *
 * @param $form_id
 *   The unique string identifying the current form.
 * @param $form
 *   An associative array containing the structure of the form.
 * @param $form_state
 *   A keyed array containing the current state of the form. This
 *   includes the current persistent storage data for the form, and
 *   any data passed along by earlier steps when displaying a
 *   multi-step form. Additional information, like the sanitized $_POST
 *   data, is also accumulated here.
 */
function drupal_process_form($form_id, &$form, &$form_state) {
  $form_state['values'] = array();

  // With $_GET, these forms are always submitted if requested.
  if ($form_state['method'] == 'get' && !empty($form_state['always_process'])) {
    if (!isset($form_state['input']['form_build_id'])) {
      $form_state['input']['form_build_id'] = $form['#build_id'];
    }
    if (!isset($form_state['input']['form_id'])) {
      $form_state['input']['form_id'] = $form_id;
    }
    if (!isset($form_state['input']['form_token']) && isset($form['#token'])) {
      $form_state['input']['form_token'] = drupal_get_token($form['#token']);
    }
  }

  // form_builder() finishes building the form by calling element #process
  // functions and mapping user input, if any, to #value properties, and also
  // storing the values in $form_state['values']. We need to retain the
  // unprocessed $form in case it needs to be cached.
  $unprocessed_form = $form;
  $form = form_builder($form_id, $form, $form_state);

  // Only process the input if we have a correct form submission.
  if ($form_state['process_input']) {
    drupal_validate_form($form_id, $form, $form_state);

    // drupal_html_id() maintains a cache of element IDs it has seen,
    // so it can prevent duplicates. We want to be sure we reset that
    // cache when a form is processed, so scenarios that result in
    // the form being built behind the scenes and again for the
    // browser don't increment all the element IDs needlessly.
    if (!form_get_errors()) {
      // In case of errors, do not break HTML IDs of other forms.
      drupal_static_reset('drupal_html_id');
    }

    if ($form_state['submitted'] && !form_get_errors() && !$form_state['rebuild']) {
      // Execute form submit handlers.
      form_execute_handlers('submit', $form, $form_state);

      // If batches were set in the submit handlers, we process them now,
      // possibly ending execution. We make sure we do not react to the batch
      // that is already being processed (if a batch operation performs a
      // drupal_form_submit).
      if ($batch =& batch_get() && !isset($batch['current_set'])) {
        // Store $form_state information in the batch definition.
        // We need the full $form_state when either:
        // - Some submit handlers were saved to be called during batch
        //   processing. See form_execute_handlers().
        // - The form is multistep.
        // In other cases, we only need the information expected by
        // drupal_redirect_form().
        if ($batch['has_form_submits'] || !empty($form_state['rebuild'])) {
          $batch['form_state'] = $form_state;
        }
        else {
          $batch['form_state'] = array_intersect_key($form_state, array_flip(array('programmed', 'rebuild', 'storage', 'no_redirect', 'redirect')));
        }

        $batch['progressive'] = !$form_state['programmed'];
        batch_process();

        // Execution continues only for programmatic forms.
        // For 'regular' forms, we get redirected to the batch processing
        // page. Form redirection will be handled in _batch_finished(),
        // after the batch is processed.
      }

      // Set a flag to indicate the the form has been processed and executed.
      $form_state['executed'] = TRUE;

      // Redirect the form based on values in $form_state.
      drupal_redirect_form($form_state);
    }

    // Don't rebuild or cache form submissions invoked via drupal_form_submit().
    if (!empty($form_state['programmed'])) {
      return;
    }

    // If $form_state['rebuild'] has been set and input has been processed
    // without validation errors, we are in a multi-step workflow that is not
    // yet complete. A new $form needs to be constructed based on the changes
    // made to $form_state during this request. Normally, a submit handler sets
    // $form_state['rebuild'] if a fully executed form requires another step.
    // However, for forms that have not been fully executed (e.g., Ajax
    // submissions triggered by non-buttons), there is no submit handler to set
    // $form_state['rebuild']. It would not make sense to redisplay the
    // identical form without an error for the user to correct, so we also
    // rebuild error-free non-executed forms, regardless of
    // $form_state['rebuild'].
    // @todo D8: Simplify this logic; considering Ajax and non-HTML front-ends,
    //   along with element-level #submit properties, it makes no sense to have
    //   divergent form execution based on whether the triggering element has
    //   #executes_submit_callback set to TRUE.
    if (($form_state['rebuild'] || !$form_state['executed']) && !form_get_errors()) {
      // Form building functions (e.g., _form_builder_handle_input_element())
      // may use $form_state['rebuild'] to determine if they are running in the
      // context of a rebuild, so ensure it is set.
      $form_state['rebuild'] = TRUE;
      $form = drupal_rebuild_form($form_id, $form_state, $form);
    }
  }

  // After processing the form, the form builder or a #process callback may
  // have set $form_state['cache'] to indicate that the form and form state
  // shall be cached. But the form may only be cached if the 'no_cache' property
  // is not set to TRUE. Only cache $form as it was prior to form_builder(),
  // because form_builder() must run for each request to accommodate new user
  // input. Rebuilt forms are not cached here, because drupal_rebuild_form()
  // already takes care of that.
  if (!$form_state['rebuild'] && $form_state['cache'] && empty($form_state['no_cache'])) {
    form_set_cache($form['#build_id'], $unprocessed_form, $form_state);
  }
}

/**
 * Prepares a structured form array.
 *
 * Adds required elements, executes any hook_form_alter functions, and
 * optionally inserts a validation token to prevent tampering.
 *
 * @param $form_id
 *   A unique string identifying the form for validation, submission,
 *   theming, and hook_form_alter functions.
 * @param $form
 *   An associative array containing the structure of the form.
 * @param $form_state
 *   A keyed array containing the current state of the form. Passed
 *   in here so that hook_form_alter() calls can use it, as well.
 */
function drupal_prepare_form($form_id, &$form, &$form_state) {
  global $user;

  $form['#type'] = 'form';
  $form_state['programmed'] = isset($form_state['programmed']) ? $form_state['programmed'] : FALSE;

  // Fix the form method, if it is 'get' in $form_state, but not in $form.
  if ($form_state['method'] == 'get' && !isset($form['#method'])) {
    $form['#method'] = 'get';
  }

  // Generate a new #build_id for this form, if none has been set already. The
  // form_build_id is used as key to cache a particular build of the form. For
  // multi-step forms, this allows the user to go back to an earlier build, make
  // changes, and re-submit.
  // @see drupal_build_form()
  // @see drupal_rebuild_form()
  if (!isset($form['#build_id'])) {
    $form['#build_id'] = 'form-' . Crypt::hashBase64(uniqid(mt_rand(), TRUE) . mt_rand());
  }
  $form['form_build_id'] = array(
    '#type' => 'hidden',
    '#value' => $form['#build_id'],
    '#id' => $form['#build_id'],
    '#name' => 'form_build_id',
    // Form processing and validation requires this value, so ensure the
    // submitted form value appears literally, regardless of custom #tree
    // and #parents being set elsewhere.
    '#parents' => array('form_build_id'),
  );

  // Add a token, based on either #token or form_id, to any form displayed to
  // authenticated users. This ensures that any submitted form was actually
  // requested previously by the user and protects against cross site request
  // forgeries.
  // This does not apply to programmatically submitted forms. Furthermore, since
  // tokens are session-bound and forms displayed to anonymous users are very
  // likely cached, we cannot assign a token for them.
  // During installation, there is no $user yet.
  if (!empty($user->uid) && !$form_state['programmed']) {
    // Form constructors may explicitly set #token to FALSE when cross site
    // request forgery is irrelevant to the form, such as search forms.
    if (isset($form['#token']) && $form['#token'] === FALSE) {
      unset($form['#token']);
    }
    // Otherwise, generate a public token based on the form id.
    else {
      $form['#token'] = $form_id;
      $form['form_token'] = array(
        '#id' => drupal_html_id('edit-' . $form_id . '-form-token'),
        '#type' => 'token',
        '#default_value' => drupal_get_token($form['#token']),
        // Form processing and validation requires this value, so ensure the
        // submitted form value appears literally, regardless of custom #tree
        // and #parents being set elsewhere.
        '#parents' => array('form_token'),
      );
    }
  }

  if (isset($form_id)) {
    $form['form_id'] = array(
      '#type' => 'hidden',
      '#value' => $form_id,
      '#id' => drupal_html_id("edit-$form_id"),
      // Form processing and validation requires this value, so ensure the
      // submitted form value appears literally, regardless of custom #tree
      // and #parents being set elsewhere.
      '#parents' => array('form_id'),
    );
  }
  if (!isset($form['#id'])) {
    $form['#id'] = drupal_html_id($form_id);
  }

  $form += element_info('form');
  $form += array('#tree' => FALSE, '#parents' => array());

  if (!isset($form['#validate'])) {
    // Ensure that modules can rely on #validate being set.
    $form['#validate'] = array();
    if (isset($form_state['build_info']['callback_object'])) {
      $form['#validate'][] = array($form_state['build_info']['callback_object'], 'validateForm');
    }
    // Check for a handler specific to $form_id.
    elseif (function_exists($form_id . '_validate')) {
      $form['#validate'][] = $form_id . '_validate';
    }
    // Otherwise check whether this is a shared form and whether there is a
    // handler for the shared $form_id.
    elseif (isset($form_state['build_info']['base_form_id']) && function_exists($form_state['build_info']['base_form_id'] . '_validate')) {
      $form['#validate'][] = $form_state['build_info']['base_form_id'] . '_validate';
    }
  }

  if (!isset($form['#submit'])) {
    // Ensure that modules can rely on #submit being set.
    $form['#submit'] = array();
    if (isset($form_state['build_info']['callback_object'])) {
      $form['#submit'][] = array($form_state['build_info']['callback_object'], 'submitForm');
    }
    // Check for a handler specific to $form_id.
    elseif (function_exists($form_id . '_submit')) {
      $form['#submit'][] = $form_id . '_submit';
    }
    // Otherwise check whether this is a shared form and whether there is a
    // handler for the shared $form_id.
    elseif (isset($form_state['build_info']['base_form_id']) && function_exists($form_state['build_info']['base_form_id'] . '_submit')) {
      $form['#submit'][] = $form_state['build_info']['base_form_id'] . '_submit';
    }
  }

  // If no #theme has been set, automatically apply theme suggestions.
  // theme_form() itself is in #theme_wrappers and not #theme. Therefore, the
  // #theme function only has to care for rendering the inner form elements,
  // not the form itself.
  if (!isset($form['#theme'])) {
    $form['#theme'] = array($form_id);
    if (isset($form_state['build_info']['base_form_id'])) {
      $form['#theme'][] = $form_state['build_info']['base_form_id'];
    }
  }

  // Invoke hook_form_alter(), hook_form_BASE_FORM_ID_alter(), and
  // hook_form_FORM_ID_alter() implementations.
  $hooks = array('form');
  if (isset($form_state['build_info']['base_form_id'])) {
    $hooks[] = 'form_' . $form_state['build_info']['base_form_id'];
  }
  $hooks[] = 'form_' . $form_id;
  drupal_alter($hooks, $form, $form_state, $form_id);
}


/**
 * Validates user-submitted form data in the $form_state array.
 *
 * @param $form_id
 *   A unique string identifying the form for validation, submission,
 *   theming, and hook_form_alter functions.
 * @param $form
 *   An associative array containing the structure of the form, which is passed
 *   by reference. Form validation handlers are able to alter the form structure
 *   (like #process and #after_build callbacks during form building) in case of
 *   a validation error. If a validation handler alters the form structure, it
 *   is responsible for validating the values of changed form elements in
 *   $form_state['values'] to prevent form submit handlers from receiving
 *   unvalidated values.
 * @param $form_state
 *   A keyed array containing the current state of the form. The current
 *   user-submitted data is stored in $form_state['values'], though
 *   form validation functions are passed an explicit copy of the
 *   values for the sake of simplicity. Validation handlers can also use
 *   $form_state to pass information on to submit handlers. For example:
 *     $form_state['data_for_submission'] = $data;
 *   This technique is useful when validation requires file parsing,
 *   web service requests, or other expensive requests that should
 *   not be repeated in the submission step.
 */
function drupal_validate_form($form_id, &$form, &$form_state) {
  $validated_forms = &drupal_static(__FUNCTION__, array());

  if (isset($validated_forms[$form_id]) && empty($form_state['must_validate'])) {
    return;
  }

  // If the session token was set by drupal_prepare_form(), ensure that it
  // matches the current user's session.
  if (isset($form['#token'])) {
    if (!drupal_valid_token($form_state['values']['form_token'], $form['#token'])) {
      $path = current_path();
      $query = drupal_get_query_parameters();
      $url = url($path, array('query' => $query));

      // Setting this error will cause the form to fail validation.
      form_set_error('form_token', t('The form has become outdated. Copy any unsaved work in the form below and then <a href="@link">reload this page</a>.', array('@link' => $url)));
    }
  }

  _form_validate($form, $form_state, $form_id);
  $validated_forms[$form_id] = TRUE;

  // If validation errors are limited then remove any non validated form values,
  // so that only values that passed validation are left for submit callbacks.
  if (isset($form_state['triggering_element']['#limit_validation_errors']) && $form_state['triggering_element']['#limit_validation_errors'] !== FALSE) {
    $values = array();
    foreach ($form_state['triggering_element']['#limit_validation_errors'] as $section) {
      // If the section exists within $form_state['values'], even if the value
      // is NULL, copy it to $values.
      $section_exists = NULL;
      $value = NestedArray::getValue($form_state['values'], $section, $section_exists);
      if ($section_exists) {
        NestedArray::setValue($values, $section, $value);
      }
    }
    // A button's #value does not require validation, so for convenience we
    // allow the value of the clicked button to be retained in its normal
    // $form_state['values'] locations, even if these locations are not included
    // in #limit_validation_errors.
    if (!empty($form_state['triggering_element']['#is_button'])) {
      $button_value = $form_state['triggering_element']['#value'];

      // Like all input controls, the button value may be in the location
      // dictated by #parents. If it is, copy it to $values, but do not override
      // what may already be in $values.
      $parents = $form_state['triggering_element']['#parents'];
      if (!NestedArray::keyExists($values, $parents) && NestedArray::getValue($form_state['values'], $parents) === $button_value) {
        NestedArray::setValue($values, $parents, $button_value);
      }

      // Additionally, form_builder() places the button value in
      // $form_state['values'][BUTTON_NAME]. If it's still there, after
      // validation handlers have run, copy it to $values, but do not override
      // what may already be in $values.
      $name = $form_state['triggering_element']['#name'];
      if (!isset($values[$name]) && isset($form_state['values'][$name]) && $form_state['values'][$name] === $button_value) {
        $values[$name] = $button_value;
      }
    }
    $form_state['values'] = $values;
  }
}

/**
 * Redirects the user to a URL after a form has been processed.
 *
 * After a form is submitted and processed, normally the user should be
 * redirected to a new destination page. This function figures out what that
 * destination should be, based on the $form_state array and the 'destination'
 * query string in the request URL, and redirects the user there.
 *
 * Usually (for exceptions, see below) $form_state['redirect'] determines where
 * to redirect the user. This can be set either to a string (the path to
 * redirect to), or an array of arguments for drupal_goto(). If
 * $form_state['redirect'] is missing, the user is usually (again, see below for
 * exceptions) redirected back to the page they came from, where they should see
 * a fresh, unpopulated copy of the form.
 *
 * Here is an example of how to set up a form to redirect to the path 'node':
 * @code
 * $form_state['redirect'] = 'node';
 * @endcode
 * And here is an example of how to redirect to 'node/123?foo=bar#baz':
 * @code
 * $form_state['redirect'] = array(
 *   'node/123',
 *   array(
 *     'query' => array(
 *       'foo' => 'bar',
 *     ),
 *     'fragment' => 'baz',
 *   ),
 * );
 * @endcode
 *
 * There are several exceptions to the "usual" behavior described above:
 * - If $form_state['programmed'] is TRUE, the form submission was usually
 *   invoked via drupal_form_submit(), so any redirection would break the script
 *   that invoked drupal_form_submit() and no redirection is done.
 * - If $form_state['rebuild'] is TRUE, the form is being rebuilt, and no
 *   redirection is done.
 * - If $form_state['no_redirect'] is TRUE, redirection is disabled. This is
 *   set, for instance, by ajax_get_form() to prevent redirection in Ajax
 *   callbacks. $form_state['no_redirect'] should never be set or altered by
 *   form builder functions or form validation/submit handlers.
 * - If $form_state['redirect'] is set to FALSE, redirection is disabled.
 * - If none of the above conditions has prevented redirection, then the
 *   redirect is accomplished by calling drupal_goto(), passing in the value of
 *   $form_state['redirect'] if it is set, or the current path if it is
 *   not. drupal_goto() preferentially uses the value of $_GET['destination']
 *   (the 'destination' URL query string) if it is present, so this will
 *   override any values set by $form_state['redirect']. Note that during
 *   installation, install_goto() is called in place of drupal_goto().
 *
 * @param $form_state
 *   An associative array containing the current state of the form.
 *
 * @see drupal_process_form()
 * @see drupal_build_form()
 */
function drupal_redirect_form($form_state) {
  // Skip redirection for form submissions invoked via drupal_form_submit().
  if (!empty($form_state['programmed'])) {
    return;
  }
  // Skip redirection if rebuild is activated.
  if (!empty($form_state['rebuild'])) {
    return;
  }
  // Skip redirection if it was explicitly disallowed.
  if (!empty($form_state['no_redirect'])) {
    return;
  }
  // Only invoke drupal_goto() if redirect value was not set to FALSE.
  if (!isset($form_state['redirect']) || $form_state['redirect'] !== FALSE) {
    if (isset($form_state['redirect'])) {
      if (is_array($form_state['redirect'])) {
        call_user_func_array('drupal_goto', $form_state['redirect']);
      }
      else {
        // This function can be called from the installer, which guarantees
        // that $redirect will always be a string, so catch that case here
        // and use the appropriate redirect function.
        $function = drupal_installation_attempted() ? 'install_goto' : 'drupal_goto';
        $function($form_state['redirect']);
      }
    }
    drupal_goto(current_path(), array('query' => drupal_container()->get('request')->query->all()));
  }
}

/**
 * Performs validation on form elements.
 *
 * First ensures required fields are completed, #maxlength is not exceeded, and
 * selected options were in the list of options given to the user. Then calls
 * user-defined validators.
 *
 * @param $elements
 *   An associative array containing the structure of the form.
 * @param $form_state
 *   A keyed array containing the current state of the form. The current
 *   user-submitted data is stored in $form_state['values'], though
 *   form validation functions are passed an explicit copy of the
 *   values for the sake of simplicity. Validation handlers can also
 *   $form_state to pass information on to submit handlers. For example:
 *     $form_state['data_for_submission'] = $data;
 *   This technique is useful when validation requires file parsing,
 *   web service requests, or other expensive requests that should
 *   not be repeated in the submission step.
 * @param $form_id
 *   A unique string identifying the form for validation, submission,
 *   theming, and hook_form_alter functions.
 */
function _form_validate(&$elements, &$form_state, $form_id = NULL) {
  // Also used in the installer, pre-database setup.
  $t = get_t();

  // Recurse through all children.
  foreach (element_children($elements) as $key) {
    if (isset($elements[$key]) && $elements[$key]) {
      _form_validate($elements[$key], $form_state);
    }
  }

  // Validate the current input.
  if (!isset($elements['#validated']) || !$elements['#validated']) {
    // The following errors are always shown.
    if (isset($elements['#needs_validation'])) {
      // Verify that the value is not longer than #maxlength.
      if (isset($elements['#maxlength']) && drupal_strlen($elements['#value']) > $elements['#maxlength']) {
        form_error($elements, $t('!name cannot be longer than %max characters but is currently %length characters long.', array('!name' => empty($elements['#title']) ? $elements['#parents'][0] : $elements['#title'], '%max' => $elements['#maxlength'], '%length' => drupal_strlen($elements['#value']))));
      }

      if (isset($elements['#options']) && isset($elements['#value'])) {
        if ($elements['#type'] == 'select') {
          $options = form_options_flatten($elements['#options']);
        }
        else {
          $options = $elements['#options'];
        }
        if (is_array($elements['#value'])) {
          $value = in_array($elements['#type'], array('checkboxes', 'tableselect')) ? array_keys($elements['#value']) : $elements['#value'];
          foreach ($value as $v) {
            if (!isset($options[$v])) {
              form_error($elements, $t('An illegal choice has been detected. Please contact the site administrator.'));
              watchdog('form', 'Illegal choice %choice in !name element.', array('%choice' => $v, '!name' => empty($elements['#title']) ? $elements['#parents'][0] : $elements['#title']), WATCHDOG_ERROR);
            }
          }
        }
        // Non-multiple select fields always have a value in HTML. If the user
        // does not change the form, it will be the value of the first option.
        // Because of this, form validation for the field will almost always
        // pass, even if the user did not select anything. To work around this
        // browser behavior, required select fields without a #default_value get
        // an additional, first empty option. In case the submitted value is
        // identical to the empty option's value, we reset the element's value
        // to NULL to trigger the regular #required handling below.
        // @see form_process_select()
        elseif ($elements['#type'] == 'select' && !$elements['#multiple'] && $elements['#required'] && !isset($elements['#default_value']) && $elements['#value'] === $elements['#empty_value']) {
          $elements['#value'] = NULL;
          form_set_value($elements, NULL, $form_state);
        }
        elseif (!isset($options[$elements['#value']])) {
          form_error($elements, $t('An illegal choice has been detected. Please contact the site administrator.'));
          watchdog('form', 'Illegal choice %choice in %name element.', array('%choice' => $elements['#value'], '%name' => empty($elements['#title']) ? $elements['#parents'][0] : $elements['#title']), WATCHDOG_ERROR);
        }
      }
    }

    // While this element is being validated, it may be desired that some calls
    // to form_set_error() be suppressed and not result in a form error, so
    // that a button that implements low-risk functionality (such as "Previous"
    // or "Add more") that doesn't require all user input to be valid can still
    // have its submit handlers triggered. The triggering element's
    // #limit_validation_errors property contains the information for which
    // errors are needed, and all other errors are to be suppressed. The
    // #limit_validation_errors property is ignored if submit handlers will run,
    // but the element doesn't have a #submit property, because it's too large a
    // security risk to have any invalid user input when executing form-level
    // submit handlers.
    if (isset($form_state['triggering_element']['#limit_validation_errors']) && ($form_state['triggering_element']['#limit_validation_errors'] !== FALSE) && !($form_state['submitted'] && !isset($form_state['triggering_element']['#submit']))) {
      form_set_error(NULL, '', $form_state['triggering_element']['#limit_validation_errors']);
    }
    // If submit handlers won't run (due to the submission having been triggered
    // by an element whose #executes_submit_callback property isn't TRUE), then
    // it's safe to suppress all validation errors, and we do so by default,
    // which is particularly useful during an Ajax submission triggered by a
    // non-button. An element can override this default by setting the
    // #limit_validation_errors property. For button element types,
    // #limit_validation_errors defaults to FALSE (via system_element_info()),
    // so that full validation is their default behavior.
    elseif (isset($form_state['triggering_element']) && !isset($form_state['triggering_element']['#limit_validation_errors']) && !$form_state['submitted']) {
      form_set_error(NULL, '', array());
    }
    // As an extra security measure, explicitly turn off error suppression if
    // one of the above conditions wasn't met. Since this is also done at the
    // end of this function, doing it here is only to handle the rare edge case
    // where a validate handler invokes form processing of another form.
    else {
      drupal_static_reset('form_set_error:limit_validation_errors');
    }

    // Make sure a value is passed when the field is required.
    if (isset($elements['#needs_validation']) && $elements['#required']) {
      // A simple call to empty() will not cut it here as some fields, like
      // checkboxes, can return a valid value of '0'. Instead, check the
      // length if it's a string, and the item count if it's an array.
      // An unchecked checkbox has a #value of integer 0, different than string
      // '0', which could be a valid value.
      $is_empty_multiple = (!count($elements['#value']));
      $is_empty_string = (is_string($elements['#value']) && drupal_strlen(trim($elements['#value'])) == 0);
      $is_empty_value = ($elements['#value'] === 0);
      if ($is_empty_multiple || $is_empty_string || $is_empty_value) {
        // Flag this element as #required_but_empty to allow #element_validate
        // handlers to set a custom required error message, but without having
        // to re-implement the complex logic to figure out whether the field
        // value is empty.
        $elements['#required_but_empty'] = TRUE;
      }
    }

    // Call user-defined form level validators.
    if (isset($form_id)) {
      form_execute_handlers('validate', $elements, $form_state);
    }
    // Call any element-specific validators. These must act on the element
    // #value data.
    elseif (isset($elements['#element_validate'])) {
      foreach ($elements['#element_validate'] as $callback) {
        call_user_func_array($callback, array(&$elements, &$form_state, &$form_state['complete_form']));
      }
    }

    // Ensure that a #required form error is thrown, regardless of whether
    // #element_validate handlers changed any properties. If $is_empty_value
    // is defined, then above #required validation code ran, so the other
    // variables are also known to be defined and we can test them again.
    if (isset($is_empty_value) && ($is_empty_multiple || $is_empty_string || $is_empty_value)) {
      if (isset($elements['#required_error'])) {
        form_error($elements, $elements['#required_error']);
      }
      // A #title is not mandatory for form elements, but without it we cannot
      // set a form error message. So when a visible title is undesirable, form
      // constructors are encouraged to set #title anyway, and then set
      // #title_display to 'invisible'. This improves accessibility.
      elseif (isset($elements['#title'])) {
        form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
      }
      else {
        form_error($elements);
      }
    }

    $elements['#validated'] = TRUE;
  }

  // Done validating this element, so turn off error suppression.
  // _form_validate() turns it on again when starting on the next element, if
  // it's still appropriate to do so.
  drupal_static_reset('form_set_error:limit_validation_errors');
}

/**
 * Executes custom validation and submission handlers for a given form.
 *
 * Button-specific handlers are checked first. If none exist, the function
 * falls back to form-level handlers.
 *
 * @param $type
 *   The type of handler to execute. 'validate' or 'submit' are the
 *   defaults used by Form API.
 * @param $form
 *   An associative array containing the structure of the form.
 * @param $form_state
 *   A keyed array containing the current state of the form. If the user
 *   submitted the form by clicking a button with custom handler functions
 *   defined, those handlers will be stored here.
 */
function form_execute_handlers($type, &$form, &$form_state) {
  // If there was a button pressed, use its handlers.
  if (isset($form_state[$type . '_handlers'])) {
    $handlers = $form_state[$type . '_handlers'];
  }
  // Otherwise, check for a form-level handler.
  elseif (isset($form['#' . $type])) {
    $handlers = $form['#' . $type];
  }
  else {
    $handlers = array();
  }

  foreach ($handlers as $function) {
    // Check if a previous _submit handler has set a batch, but make sure we
    // do not react to a batch that is already being processed (for instance
    // if a batch operation performs a drupal_form_submit()).
    if ($type == 'submit' && ($batch =& batch_get()) && !isset($batch['id'])) {
      // Some previous submit handler has set a batch. To ensure correct
      // execution order, store the call in a special 'control' batch set.
      // See _batch_next_set().
      $batch['sets'][] = array('form_submit' => $function);
      $batch['has_form_submits'] = TRUE;
    }
    else {
      call_user_func_array($function, array(&$form, &$form_state));
    }
  }
}

/**
 * Files an error against a form element.
 *
 * When a validation error is detected, the validator calls form_set_error() to
 * indicate which element needs to be changed and provide an error message. This
 * causes the Form API to not execute the form submit handlers, and instead to
 * re-display the form to the user with the corresponding elements rendered with
 * an 'error' CSS class (shown as red by default).
 *
 * The standard form_set_error() behavior can be changed if a button provides
 * the #limit_validation_errors property. Multistep forms not wanting to
 * validate the whole form can set #limit_validation_errors on buttons to
 * limit validation errors to only certain elements. For example, pressing the
 * "Previous" button in a multistep form should not fire validation errors just
 * because the current step has invalid values. If #limit_validation_errors is
 * set on a clicked button, the button must also define a #submit property
 * (may be set to an empty array). Any #submit handlers will be executed even if
 * there is invalid input, so extreme care should be taken with respect to any
 * actions taken by them. This is typically not a problem with buttons like
 * "Previous" or "Add more" that do not invoke persistent storage of the
 * submitted form values. Do not use the #limit_validation_errors property on
 * buttons that trigger saving of form values to the database.
 *
 * The #limit_validation_errors property is a list of "sections" within
 * $form_state['values'] that must contain valid values. Each "section" is an
 * array with the ordered set of keys needed to reach that part of
 * $form_state['values'] (i.e., the #parents property of the element).
 *
 * Example 1: Allow the "Previous" button to function, regardless of whether any
 * user input is valid.
 *
 * @code
 *   $form['actions']['previous'] = array(
 *     '#type' => 'submit',
 *     '#value' => t('Previous'),
 *     '#limit_validation_errors' => array(),       // No validation.
 *     '#submit' => array('some_submit_function'),  // #submit required.
 *   );
 * @endcode
 *
 * Example 2: Require some, but not all, user input to be valid to process the
 * submission of a "Previous" button.
 *
 * @code
 *   $form['actions']['previous'] = array(
 *     '#type' => 'submit',
 *     '#value' => t('Previous'),
 *     '#limit_validation_errors' => array(
 *       array('step1'),       // Validate $form_state['values']['step1'].
 *       array('foo', 'bar'),  // Validate $form_state['values']['foo']['bar'].
 *     ),
 *     '#submit' => array('some_submit_function'), // #submit required.
 *   );
 * @endcode
 *
 * This will require $form_state['values']['step1'] and everything within it
 * (for example, $form_state['values']['step1']['choice']) to be valid, so
 * calls to form_set_error('step1', $message) or
 * form_set_error('step1][choice', $message) will prevent the submit handlers
 * from running, and result in the error message being displayed to the user.
 * However, calls to form_set_error('step2', $message) and
 * form_set_error('step2][groupX][choiceY', $message) will be suppressed,
 * resulting in the message not being displayed to the user, and the submit
 * handlers will run despite $form_state['values']['step2'] and
 * $form_state['values']['step2']['groupX']['choiceY'] containing invalid
 * values. Errors for an invalid $form_state['values']['foo'] will be
 * suppressed, but errors flagging invalid values for
 * $form_state['values']['foo']['bar'] and everything within it will be
 * flagged and submission prevented.
 *
 * Partial form validation is implemented by suppressing errors rather than by
 * skipping the input processing and validation steps entirely, because some
 * forms have button-level submit handlers that call Drupal API functions that
 * assume that certain data exists within $form_state['values'], and while not
 * doing anything with that data that requires it to be valid, PHP errors
 * would be triggered if the input processing and validation steps were fully
 * skipped.
 *
 * @param $name
 *   The name of the form element. If the #parents property of your form
 *   element is array('foo', 'bar', 'baz') then you may set an error on 'foo'
 *   or 'foo][bar][baz'. Setting an error on 'foo' sets an error for every
 *   element where the #parents array starts with 'foo'.
 * @param $message
 *   The error message to present to the user.
 * @param $limit_validation_errors
 *   Internal use only. The #limit_validation_errors property of the clicked
 *   button, if it exists.
 *
 * @return
 *   Return value is for internal use only. To get a list of errors, use
 *   form_get_errors() or form_get_error().
 *
 * @see http://drupal.org/node/370537
 * @see http://drupal.org/node/763376
 */
function form_set_error($name = NULL, $message = '', $limit_validation_errors = NULL) {
  $form = &drupal_static(__FUNCTION__, array());
  $sections = &drupal_static(__FUNCTION__ . ':limit_validation_errors');
  if (isset($limit_validation_errors)) {
    $sections = $limit_validation_errors;
  }

  if (isset($name) && !isset($form[$name])) {
    $record = TRUE;
    if (isset($sections)) {
      // #limit_validation_errors is an array of "sections" within which user
      // input must be valid. If the element is within one of these sections,
      // the error must be recorded. Otherwise, it can be suppressed.
      // #limit_validation_errors can be an empty array, in which case all
      // errors are suppressed. For example, a "Previous" button might want its
      // submit action to be triggered even if none of the submitted values are
      // valid.
      $record = FALSE;
      foreach ($sections as $section) {
        // Exploding by '][' reconstructs the element's #parents. If the
        // reconstructed #parents begin with the same keys as the specified
        // section, then the element's values are within the part of
        // $form_state['values'] that the clicked button requires to be valid,
        // so errors for this element must be recorded. As the exploded array
        // will all be strings, we need to cast every value of the section
        // array to string.
        if (array_slice(explode('][', $name), 0, count($section)) === array_map('strval', $section)) {
          $record = TRUE;
          break;
        }
      }
    }
    if ($record) {
      $form[$name] = $message;
      if ($message) {
        drupal_set_message($message, 'error');
      }
    }
  }

  return $form;
}

/**
 * Clears all errors against all form elements made by form_set_error().
 */
function form_clear_error() {
  drupal_static_reset('form_set_error');
}

/**
 * Returns an associative array of all errors.
 */
function form_get_errors() {
  $form = form_set_error();
  if (!empty($form)) {
    return $form;
  }
}

/**
 * Returns the error message filed against the given form element.
 *
 * Form errors higher up in the form structure override deeper errors as well as
 * errors on the element itself.
 */
function form_get_error($element) {
  $form = form_set_error();
  $parents = array();
  foreach ($element['#parents'] as $parent) {
    $parents[] = $parent;
    $key = implode('][', $parents);
    if (isset($form[$key])) {
      return $form[$key];
    }
  }
}

/**
 * Flags an element as having an error.
 */
function form_error(&$element, $message = '') {
  form_set_error(implode('][', $element['#parents']), $message);
}

/**
 * Builds and processes all elements in the structured form array.
 *
 * Adds any required properties to each element, maps the incoming input data
 * to the proper elements, and executes any #process handlers attached to a
 * specific element.
 *
 * This is one of the three primary functions that recursively iterates a form
 * array. This one does it for completing the form building process. The other
 * two are _form_validate() (invoked via drupal_validate_form() and used to
 * invoke validation logic for each element) and drupal_render() (for rendering
 * each element). Each of these three pipelines provides ample opportunity for
 * modules to customize what happens. For example, during this function's life
 * cycle, the following functions get called for each element:
 * - $element['#value_callback']: A function that implements how user input is
 *   mapped to an element's #value property. This defaults to a function named
 *   'form_type_TYPE_value' where TYPE is $element['#type'].
 * - $element['#process']: An array of functions called after user input has
 *   been mapped to the element's #value property. These functions can be used
 *   to dynamically add child elements: for example, for the 'date' element
 *   type, one of the functions in this array is form_process_datetime(), which adds
 *   the individual 'date', and 'time'. child elements. These functions
 *   can also be used to set additional properties or implement special logic
 *   other than adding child elements: for example, for the 'details' element
 *   type, one of the functions in this array is form_process_details(), which
 *   adds the attributes and JavaScript needed to make the details work in older
 *   browsers. The #process functions are called in preorder traversal, meaning
 *   they are called for the parent element first, then for the child elements.
 * - $element['#after_build']: An array of functions called after form_builder()
 *   is done with its processing of the element. These are called in postorder
 *   traversal, meaning they are called for the child elements first, then for
 *   the parent element.
 * There are similar properties containing callback functions invoked by
 * _form_validate() and drupal_render(), appropriate for those operations.
 *
 * Developers are strongly encouraged to integrate the functionality needed by
 * their form or module within one of these three pipelines, using the
 * appropriate callback property, rather than implementing their own recursive
 * traversal of a form array. This facilitates proper integration between
 * multiple modules. For example, module developers are familiar with the
 * relative order in which hook_form_alter() implementations and #process
 * functions run. A custom traversal function that affects the building of a
 * form is likely to not integrate with hook_form_alter() and #process in the
 * expected way. Also, deep recursion within PHP is both slow and memory
 * intensive, so it is best to minimize how often it's done.
 *
 * As stated above, each element's #process functions are executed after its
 * #value has been set. This enables those functions to execute conditional
 * logic based on the current value. However, all of form_builder() runs before
 * drupal_validate_form() is called, so during #process function execution, the
 * element's #value has not yet been validated, so any code that requires
 * validated values must reside within a submit handler.
 *
 * As a security measure, user input is used for an element's #value only if the
 * element exists within $form, is not disabled (as per the #disabled property),
 * and can be accessed (as per the #access property, except that forms submitted
 * using drupal_form_submit() bypass #access restrictions). When user input is
 * ignored due to #disabled and #access restrictions, the element's default
 * value is used.
 *
 * Because of the preorder traversal, where #process functions of an element run
 * before user input for its child elements is processed, and because of the
 * Form API security of user input processing with respect to #access and
 * #disabled described above, this generally means that #process functions
 * should not use an element's (unvalidated) #value to affect the #disabled or
 * #access of child elements. Use-cases where a developer may be tempted to
 * implement such conditional logic usually fall into one of two categories:
 * - Where user input from the current submission must affect the structure of a
 *   form, including properties like #access and #disabled that affect how the
 *   next submission needs to be processed, a multi-step workflow is needed.
 *   This is most commonly implemented with a submit handler setting persistent
 *   data within $form_state based on *validated* values in
 *   $form_state['values'] and setting $form_state['rebuild']. The form building
 *   functions must then be implemented to use the $form_state data to rebuild
 *   the form with the structure appropriate for the new state.
 * - Where user input must affect the rendering of the form without affecting
 *   its structure, the necessary conditional rendering logic should reside
 *   within functions that run during the rendering phase (#pre_render, #theme,
 *   #theme_wrappers, and #post_render).
 *
 * @param $form_id
 *   A unique string identifying the form for validation, submission,
 *   theming, and hook_form_alter functions.
 * @param $element
 *   An associative array containing the structure of the current element.
 * @param $form_state
 *   A keyed array containing the current state of the form. In this
 *   context, it is used to accumulate information about which button
 *   was clicked when the form was submitted, as well as the sanitized
 *   $_POST data.
 */
function form_builder($form_id, &$element, &$form_state) {
  // Initialize as unprocessed.
  $element['#processed'] = FALSE;

  // Use element defaults.
  if (isset($element['#type']) && empty($element['#defaults_loaded']) && ($info = element_info($element['#type']))) {
    // Overlay $info onto $element, retaining preexisting keys in $element.
    $element += $info;
    $element['#defaults_loaded'] = TRUE;
  }
  // Assign basic defaults common for all form elements.
  $element += array(
    '#required' => FALSE,
    '#attributes' => array(),
    '#title_display' => 'before',
  );

  // Special handling if we're on the top level form element.
  if (isset($element['#type']) && $element['#type'] == 'form') {
    if (!empty($element['#https']) && settings()->get('mixed_mode_sessions', FALSE) &&
        !url_is_external($element['#action'])) {
      global $base_root;

      // Not an external URL so ensure that it is secure.
      $element['#action'] = str_replace('http://', 'https://', $base_root) . $element['#action'];
    }

    // Store a reference to the complete form in $form_state prior to building
    // the form. This allows advanced #process and #after_build callbacks to
    // perform changes elsewhere in the form.
    $form_state['complete_form'] = &$element;

    // Set a flag if we have a correct form submission. This is always TRUE for
    // programmed forms coming from drupal_form_submit(), or if the form_id coming
    // from the POST data is set and matches the current form_id.
    if ($form_state['programmed'] || (!empty($form_state['input']) && (isset($form_state['input']['form_id']) && ($form_state['input']['form_id'] == $form_id)))) {
      $form_state['process_input'] = TRUE;
    }
    else {
      $form_state['process_input'] = FALSE;
    }

    // All form elements should have an #array_parents property.
    $element['#array_parents'] = array();
  }

  if (!isset($element['#id'])) {
    $element['#id'] = drupal_html_id('edit-' . implode('-', $element['#parents']));
  }

  // Add the aria-describedby attribute to associate the form control with its
  // description.
  if (!empty($element['#description'])) {
    $element['#attributes']['aria-describedby'] = $element['#id'] . '--description';
  }
  // Handle input elements.
  if (!empty($element['#input'])) {
    _form_builder_handle_input_element($form_id, $element, $form_state);
  }
  // Allow for elements to expand to multiple elements, e.g., radios,
  // checkboxes and files.
  if (isset($element['#process']) && !$element['#processed']) {
    foreach ($element['#process'] as $process) {
      $element = call_user_func_array($process, array(&$element, &$form_state, &$form_state['complete_form']));
    }
    $element['#processed'] = TRUE;
  }

  // We start off assuming all form elements are in the correct order.
  $element['#sorted'] = TRUE;

  // Recurse through all child elements.
  $count = 0;
  foreach (element_children($element) as $key) {
    // Prior to checking properties of child elements, their default properties
    // need to be loaded.
    if (isset($element[$key]['#type']) && empty($element[$key]['#defaults_loaded']) && ($info = element_info($element[$key]['#type']))) {
      $element[$key] += $info;
      $element[$key]['#defaults_loaded'] = TRUE;
    }

    // Don't squash an existing tree value.
    if (!isset($element[$key]['#tree'])) {
      $element[$key]['#tree'] = $element['#tree'];
    }

    // Deny access to child elements if parent is denied.
    if (isset($element['#access']) && !$element['#access']) {
      $element[$key]['#access'] = FALSE;
    }

    // Make child elements inherit their parent's #disabled and #allow_focus
    // values unless they specify their own.
    foreach (array('#disabled', '#allow_focus') as $property) {
      if (isset($element[$property]) && !isset($element[$key][$property])) {
        $element[$key][$property] = $element[$property];
      }
    }

    // Don't squash existing parents value.
    if (!isset($element[$key]['#parents'])) {
      // Check to see if a tree of child elements is present. If so,
      // continue down the tree if required.
      $element[$key]['#parents'] = $element[$key]['#tree'] && $element['#tree'] ? array_merge($element['#parents'], array($key)) : array($key);
    }
    // Ensure #array_parents follows the actual form structure.
    $array_parents = $element['#array_parents'];
    $array_parents[] = $key;
    $element[$key]['#array_parents'] = $array_parents;

    // Assign a decimal placeholder weight to preserve original array order.
    if (!isset($element[$key]['#weight'])) {
      $element[$key]['#weight'] = $count/1000;
    }
    else {
      // If one of the child elements has a weight then we will need to sort
      // later.
      unset($element['#sorted']);
    }
    $element[$key] = form_builder($form_id, $element[$key], $form_state);
    $count++;
  }

  // The #after_build flag allows any piece of a form to be altered
  // after normal input parsing has been completed.
  if (isset($element['#after_build']) && !isset($element['#after_build_done'])) {
    foreach ($element['#after_build'] as $function) {
      $element = $function($element, $form_state);
    }
    $element['#after_build_done'] = TRUE;
  }

  // If there is a file element, we need to flip a flag so later the
  // form encoding can be set.
  if (isset($element['#type']) && $element['#type'] == 'file') {
    $form_state['has_file_element'] = TRUE;
  }

  // Final tasks for the form element after form_builder() has run for all other
  // elements.
  if (isset($element['#type']) && $element['#type'] == 'form') {
    // If there is a file element, we set the form encoding.
    if (isset($form_state['has_file_element'])) {
      $element['#attributes']['enctype'] = 'multipart/form-data';
    }

    // If a form contains a single textfield, and the ENTER key is pressed
    // within it, Internet Explorer submits the form with no POST data
    // identifying any submit button. Other browsers submit POST data as though
    // the user clicked the first button. Therefore, to be as consistent as we
    // can be across browsers, if no 'triggering_element' has been identified
    // yet, default it to the first button.
    if (!$form_state['programmed'] && !isset($form_state['triggering_element']) && !empty($form_state['buttons'])) {
      $form_state['triggering_element'] = $form_state['buttons'][0];
    }

    // If the triggering element specifies "button-level" validation and submit
    // handlers to run instead of the default form-level ones, then add those to
    // the form state.
    foreach (array('validate', 'submit') as $type) {
      if (isset($form_state['triggering_element']['#' . $type])) {
        $form_state[$type . '_handlers'] = $form_state['triggering_element']['#' . $type];
      }
    }

    // If the triggering element executes submit handlers, then set the form
    // state key that's needed for those handlers to run.
    if (!empty($form_state['triggering_element']['#executes_submit_callback'])) {
      $form_state['submitted'] = TRUE;
    }

    // Special processing if the triggering element is a button.
    if (!empty($form_state['triggering_element']['#is_button'])) {
      // Because there are several ways in which the triggering element could
      // have been determined (including from input variables set by JavaScript
      // or fallback behavior implemented for IE), and because buttons often
      // have their #name property not derived from their #parents property, we
      // can't assume that input processing that's happened up until here has
      // resulted in $form_state['values'][BUTTON_NAME] being set. But it's
      // common for forms to have several buttons named 'op' and switch on
      // $form_state['values']['op'] during submit handler execution.
      $form_state['values'][$form_state['triggering_element']['#name']] = $form_state['triggering_element']['#value'];
    }
  }
  return $element;
}

/**
 * Adds the #name and #value properties of an input element before rendering.
 */
function _form_builder_handle_input_element($form_id, &$element, &$form_state) {
  if (!isset($element['#name'])) {
    $name = array_shift($element['#parents']);
    $element['#name'] = $name;
    if ($element['#type'] == 'file') {
      // To make it easier to handle $_FILES in file.inc, we place all
      // file fields in the 'files' array. Also, we do not support
      // nested file names.
      $element['#name'] = 'files[' . $element['#name'] . ']';
    }
    elseif (count($element['#parents'])) {
      $element['#name'] .= '[' . implode('][', $element['#parents']) . ']';
    }
    array_unshift($element['#parents'], $name);
  }

  // Setting #disabled to TRUE results in user input being ignored, regardless
  // of how the element is themed or whether JavaScript is used to change the
  // control's attributes. However, it's good UI to let the user know that input
  // is not wanted for the control. HTML supports two attributes for this:
  // http://www.w3.org/TR/html401/interact/forms.html#h-17.12. If a form wants
  // to start a control off with one of these attributes for UI purposes only,
  // but still allow input to be processed if it's sumitted, it can set the
  // desired attribute in #attributes directly rather than using #disabled.
  // However, developers should think carefully about the accessibility
  // implications of doing so: if the form expects input to be enterable under
  // some condition triggered by JavaScript, how would someone who has
  // JavaScript disabled trigger that condition? Instead, developers should
  // consider whether a multi-step form would be more appropriate (#disabled can
  // be changed from step to step). If one still decides to use JavaScript to
  // affect when a control is enabled, then it is best for accessibility for the
  // control to be enabled in the HTML, and disabled by JavaScript on document
  // ready.
  if (!empty($element['#disabled'])) {
    if (!empty($element['#allow_focus'])) {
      $element['#attributes']['readonly'] = 'readonly';
    }
    else {
      $element['#attributes']['disabled'] = 'disabled';
    }
  }

  // With JavaScript or other easy hacking, input can be submitted even for
  // elements with #access=FALSE or #disabled=TRUE. For security, these must
  // not be processed. Forms that set #disabled=TRUE on an element do not
  // expect input for the element, and even forms submitted with
  // drupal_form_submit() must not be able to get around this. Forms that set
  // #access=FALSE on an element usually allow access for some users, so forms
  // submitted with drupal_form_submit() may bypass access restriction and be
  // treated as high-privilege users instead.
  $process_input = empty($element['#disabled']) && ($form_state['programmed'] || ($form_state['process_input'] && (!isset($element['#access']) || $element['#access'])));

  // Set the element's #value property.
  if (!isset($element['#value']) && !array_key_exists('#value', $element)) {
    $value_callback = !empty($element['#value_callback']) ? $element['#value_callback'] : 'form_type_' . $element['#type'] . '_value';
    if ($process_input) {
      // Get the input for the current element. NULL values in the input need to
      // be explicitly distinguished from missing input. (see below)
      $input_exists = NULL;
      $input = NestedArray::getValue($form_state['input'], $element['#parents'], $input_exists);
      // For browser-submitted forms, the submitted values do not contain values
      // for certain elements (empty multiple select, unchecked checkbox).
      // During initial form processing, we add explicit NULL values for such
      // elements in $form_state['input']. When rebuilding the form, we can
      // distinguish elements having NULL input from elements that were not part
      // of the initially submitted form and can therefore use default values
      // for the latter, if required. Programmatically submitted forms can
      // submit explicit NULL values when calling drupal_form_submit(), so we do
      // not modify $form_state['input'] for them.
      if (!$input_exists && !$form_state['rebuild'] && !$form_state['programmed']) {
        // Add the necessary parent keys to $form_state['input'] and sets the
        // element's input value to NULL.
        NestedArray::setValue($form_state['input'], $element['#parents'], NULL);
        $input_exists = TRUE;
      }
      // If we have input for the current element, assign it to the #value
      // property, optionally filtered through $value_callback.
      if ($input_exists) {
        if (function_exists($value_callback)) {
          $element['#value'] = $value_callback($element, $input, $form_state);
        }
        if (!isset($element['#value']) && isset($input)) {
          $element['#value'] = $input;
        }
      }
      // Mark all posted values for validation.
      if (isset($element['#value']) || (!empty($element['#required']))) {
        $element['#needs_validation'] = TRUE;
      }
    }
    // Load defaults.
    if (!isset($element['#value'])) {
      // Call #type_value without a second argument to request default_value handling.
      if (function_exists($value_callback)) {
        $element['#value'] = $value_callback($element, FALSE, $form_state);
      }
      // Final catch. If we haven't set a value yet, use the explicit default value.
      // Avoid image buttons (which come with garbage value), so we only get value
      // for the button actually clicked.
      if (!isset($element['#value']) && empty($element['#has_garbage_value'])) {
        $element['#value'] = isset($element['#default_value']) ? $element['#default_value'] : '';
      }
    }
  }

  // Determine which element (if any) triggered the submission of the form and
  // keep track of all the clickable buttons in the form for
  // form_state_values_clean(). Enforce the same input processing restrictions
  // as above.
  if ($process_input) {
    // Detect if the element triggered the submission via Ajax.
    if (_form_element_triggered_scripted_submission($element, $form_state)) {
      $form_state['triggering_element'] = $element;
    }

    // If the form was submitted by the browser rather than via Ajax, then it
    // can only have been triggered by a button, and we need to determine which
    // button within the constraints of how browsers provide this information.
    if (!empty($element['#is_button'])) {
      // All buttons in the form need to be tracked for
      // form_state_values_clean() and for the form_builder() code that handles
      // a form submission containing no button information in $_POST.
      $form_state['buttons'][] = $element;
      if (_form_button_was_clicked($element, $form_state)) {
        $form_state['triggering_element'] = $element;
      }
    }
  }

  // Set the element's value in $form_state['values'], but only, if its key
  // does not exist yet (a #value_callback may have already populated it).
  if (!NestedArray::keyExists($form_state['values'], $element['#parents'])) {
    form_set_value($element, $element['#value'], $form_state);
  }
}

/**
 * Detects if an element triggered the form submission via Ajax.
 *
 * This detects button or non-button controls that trigger a form submission via
 * Ajax or some other scriptable environment. These environments can set the
 * special input key '_triggering_element_name' to identify the triggering
 * element. If the name alone doesn't identify the element uniquely, the input
 * key '_triggering_element_value' may also be set to require a match on element
 * value. An example where this is needed is if there are several buttons all
 * named 'op', and only differing in their value.
 */
function _form_element_triggered_scripted_submission($element, &$form_state) {
  if (!empty($form_state['input']['_triggering_element_name']) && $element['#name'] == $form_state['input']['_triggering_element_name']) {
    if (empty($form_state['input']['_triggering_element_value']) || $form_state['input']['_triggering_element_value'] == $element['#value']) {
      return TRUE;
    }
  }
  return FALSE;
}

/**
 * Determines if a given button triggered the form submission.
 *
 * This detects button controls that trigger a form submission by being clicked
 * and having the click processed by the browser rather than being captured by
 * JavaScript. Essentially, it detects if the button's name and value are part
 * of the POST data, but with extra code to deal with the convoluted way in
 * which browsers submit data for image button clicks.
 *
 * This does not detect button clicks processed by Ajax (that is done in
 * _form_element_triggered_scripted_submission()) and it does not detect form
 * submissions from Internet Explorer in response to an ENTER key pressed in a
 * textfield (form_builder() has extra code for that).
 *
 * Because this function contains only part of the logic needed to determine
 * $form_state['triggering_element'], it should not be called from anywhere
 * other than within the Form API. Form validation and submit handlers needing
 * to know which button was clicked should get that information from
 * $form_state['triggering_element'].
 */
function _form_button_was_clicked($element, &$form_state) {
  // First detect normal 'vanilla' button clicks. Traditionally, all
  // standard buttons on a form share the same name (usually 'op'),
  // and the specific return value is used to determine which was
  // clicked. This ONLY works as long as $form['#name'] puts the
  // value at the top level of the tree of $_POST data.
  if (isset($form_state['input'][$element['#name']]) && $form_state['input'][$element['#name']] == $element['#value']) {
    return TRUE;
  }
  // When image buttons are clicked, browsers do NOT pass the form element
  // value in $_POST. Instead they pass an integer representing the
  // coordinates of the click on the button image. This means that image
  // buttons MUST have unique $form['#name'] values, but the details of
  // their $_POST data should be ignored.
  elseif (!empty($element['#has_garbage_value']) && isset($element['#value']) && $element['#value'] !== '') {
    return TRUE;
  }
  return FALSE;
}

/**
 * Removes internal Form API elements and buttons from submitted form values.
 *
 * This function can be used when a module wants to store all submitted form
 * values, for example, by serializing them into a single database column. In
 * such cases, all internal Form API values and all form button elements should
 * not be contained, and this function allows to remove them before the module
 * proceeds to storage. Next to button elements, the following internal values
 * are removed:
 * - form_id
 * - form_token
 * - form_build_id
 * - op
 *
 * @param $form_state
 *   A keyed array containing the current state of the form, including
 *   submitted form values; altered by reference.
 */
function form_state_values_clean(&$form_state) {
  // Remove internal Form API values.
  unset($form_state['values']['form_id'], $form_state['values']['form_token'], $form_state['values']['form_build_id'], $form_state['values']['op']);

  // Remove button values.
  // form_builder() collects all button elements in a form. We remove the button
  // value separately for each button element.
  foreach ($form_state['buttons'] as $button) {
    // Remove this button's value from the submitted form values by finding
    // the value corresponding to this button.
    // We iterate over the #parents of this button and move a reference to
    // each parent in $form_state['values']. For example, if #parents is:
    //   array('foo', 'bar', 'baz')
    // then the corresponding $form_state['values'] part will look like this:
    // array(
    //   'foo' => array(
    //     'bar' => array(
    //       'baz' => 'button_value',
    //     ),
    //   ),
    // )
    // We start by (re)moving 'baz' to $last_parent, so we are able unset it
    // at the end of the iteration. Initially, $values will contain a
    // reference to $form_state['values'], but in the iteration we move the
    // reference to $form_state['values']['foo'], and finally to
    // $form_state['values']['foo']['bar'], which is the level where we can
    // unset 'baz' (that is stored in $last_parent).
    $parents = $button['#parents'];
    $last_parent = array_pop($parents);
    $key_exists = NULL;
    $values = &NestedArray::getValue($form_state['values'], $parents, $key_exists);
    if ($key_exists && is_array($values)) {
      unset($values[$last_parent]);
    }
  }
}

/**
 * Determines the value for an image button form element.
 *
 * @param $form
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 *
 * @return
 *   The data that will appear in the $form_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_image_button_value($form, $input, $form_state) {
  if ($input !== FALSE) {
    if (!empty($input)) {
      // If we're dealing with Mozilla or Opera, we're lucky. It will
      // return a proper value, and we can get on with things.
      return $form['#return_value'];
    }
    else {
      // Unfortunately, in IE we never get back a proper value for THIS
      // form element. Instead, we get back two split values: one for the
      // X and one for the Y coordinates on which the user clicked the
      // button. We'll find this element in the #post data, and search
      // in the same spot for its name, with '_x'.
      $input = $form_state['input'];
      foreach (explode('[', $form['#name']) as $element_name) {
        // chop off the ] that may exist.
        if (substr($element_name, -1) == ']') {
          $element_name = substr($element_name, 0, -1);
        }

        if (!isset($input[$element_name])) {
          if (isset($input[$element_name . '_x'])) {
            return $form['#return_value'];
          }
          return NULL;
        }
        $input = $input[$element_name];
      }
      return $form['#return_value'];
    }
  }
}

/**
 * Determines the value for a checkbox form element.
 *
 * @param $form
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_checkbox_value($element, $input = FALSE) {
  if ($input === FALSE) {
    // Use #default_value as the default value of a checkbox, except change
    // NULL to 0, because _form_builder_handle_input_element() would otherwise
    // replace NULL with empty string, but an empty string is a potentially
    // valid value for a checked checkbox.
    return isset($element['#default_value']) ? $element['#default_value'] : 0;
  }
  else {
    // Checked checkboxes are submitted with a value (possibly '0' or ''):
    // http://www.w3.org/TR/html401/interact/forms.html#successful-controls.
    // For checked checkboxes, browsers submit the string version of
    // #return_value, but we return the original #return_value. For unchecked
    // checkboxes, browsers submit nothing at all, but
    // _form_builder_handle_input_element() detects this, and calls this
    // function with $input=NULL. Returning NULL from a value callback means to
    // use the default value, which is not what is wanted when an unchecked
    // checkbox is submitted, so we use integer 0 as the value indicating an
    // unchecked checkbox. Therefore, modules must not use integer 0 as a
    // #return_value, as doing so results in the checkbox always being treated
    // as unchecked. The string '0' is allowed for #return_value. The most
    // common use-case for setting #return_value to either 0 or '0' is for the
    // first option within a 0-indexed array of checkboxes, and for this,
    // form_process_checkboxes() uses the string rather than the integer.
    return isset($input) ? $element['#return_value'] : 0;
  }
}

/**
 * Determines the value for a checkboxes form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_checkboxes_value($element, $input = FALSE) {
  if ($input === FALSE) {
    $value = array();
    $element += array('#default_value' => array());
    foreach ($element['#default_value'] as $key) {
      $value[$key] = $key;
    }
    return $value;
  }
  elseif (is_array($input)) {
    // Programmatic form submissions use NULL to indicate that a checkbox
    // should be unchecked; see drupal_form_submit(). We therefore remove all
    // NULL elements from the array before constructing the return value, to
    // simulate the behavior of web browsers (which do not send unchecked
    // checkboxes to the server at all). This will not affect non-programmatic
    // form submissions, since all values in $_POST are strings.
    foreach ($input as $key => $value) {
      if (!isset($value)) {
        unset($input[$key]);
      }
    }
    return drupal_map_assoc($input);
  }
  else {
    return array();
  }
}

/**
 * Determines the value of a table form element.
 *
 * @param array $element
 *   The form element whose value is being populated.
 * @param array|false $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return array
 *   The data that will appear in the $form_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_table_value(array $element, $input = FALSE) {
  // If #multiple is FALSE, the regular default value of radio buttons is used.
  if (!empty($element['#tableselect']) && !empty($element['#multiple'])) {
    // Contrary to #type 'checkboxes', the default value of checkboxes in a
    // table is built from the array keys (instead of array values) of the
    // #default_value property.
    // @todo D8: Remove this inconsistency.
    if ($input === FALSE) {
      $element += array('#default_value' => array());
      return drupal_map_assoc(array_keys(array_filter($element['#default_value'])));
    }
    else {
      return is_array($input) ? drupal_map_assoc($input) : array();
    }
  }
}

/**
 * Form value callback: Determines the value for a #type radios form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   (optional) The incoming input to populate the form element. If FALSE, the
 *   element's default value is returned. Defaults to FALSE.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection for
 *   this element.
 */
function form_type_radios_value(&$element, $input = FALSE) {
  if ($input !== FALSE) {
    // When there's user input (including NULL), return it as the value.
    // However, if NULL is submitted, _form_builder_handle_input_element() will
    // apply the default value, and we want that validated against #options
    // unless it's empty. (An empty #default_value, such as NULL or FALSE, can
    // be used to indicate that no radio button is selected by default.)
    if (!isset($input) && !empty($element['#default_value'])) {
      $element['#needs_validation'] = TRUE;
    }
    return $input;
  }
  else {
    // For default value handling, simply return #default_value. Additionally,
    // for a NULL default value, set #has_garbage_value to prevent
    // _form_builder_handle_input_element() converting the NULL to an empty
    // string, so that code can distinguish between nothing selected and the
    // selection of a radio button whose value is an empty string.
    $value = isset($element['#default_value']) ? $element['#default_value'] : NULL;
    if (!isset($value)) {
      $element['#has_garbage_value'] = TRUE;
    }
    return $value;
  }
}

/**
 * Determines the value for a tableselect form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_tableselect_value($element, $input = FALSE) {
  // If $element['#multiple'] == FALSE, then radio buttons are displayed and
  // the default value handling is used.
  if (isset($element['#multiple']) && $element['#multiple']) {
    // Checkboxes are being displayed with the default value coming from the
    // keys of the #default_value property. This differs from the checkboxes
    // element which uses the array values.
    if ($input === FALSE) {
      $value = array();
      $element += array('#default_value' => array());
      foreach ($element['#default_value'] as $key => $flag) {
        if ($flag) {
          $value[$key] = $key;
        }
      }
      return $value;
    }
    else {
      return is_array($input) ? drupal_map_assoc($input) : array();
    }
  }
}

/**
 * Determines the value for a password_confirm form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_password_confirm_value($element, $input = FALSE) {
  if ($input === FALSE) {
    $element += array('#default_value' => array());
    return $element['#default_value'] + array('pass1' => '', 'pass2' => '');
  }
}

/**
 * Determines the value for a select form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_select_value($element, $input = FALSE) {
  if ($input !== FALSE) {
    if (isset($element['#multiple']) && $element['#multiple']) {
      // If an enabled multi-select submits NULL, it means all items are
      // unselected. A disabled multi-select always submits NULL, and the
      // default value should be used.
      if (empty($element['#disabled'])) {
        return (is_array($input)) ? drupal_map_assoc($input) : array();
      }
      else {
        return (isset($element['#default_value']) && is_array($element['#default_value'])) ? $element['#default_value'] : array();
      }
    }
    // Non-multiple select elements may have an empty option preprended to them
    // (see form_process_select()). When this occurs, usually #empty_value is
    // an empty string, but some forms set #empty_value to integer 0 or some
    // other non-string constant. PHP receives all submitted form input as
    // strings, but if the empty option is selected, set the value to match the
    // empty value exactly.
    elseif (isset($element['#empty_value']) && $input === (string) $element['#empty_value']) {
      return $element['#empty_value'];
    }
    else {
      return $input;
    }
  }
}

/**
 * Determines the value for a textfield form element.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_textfield_value($element, $input = FALSE) {
  if ($input !== FALSE && $input !== NULL) {
    // Equate $input to the form value to ensure it's marked for
    // validation.
    return str_replace(array("\r", "\n"), '', $input);
  }
}

/**
 * Determines the value for form's token value.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE,
 *   the element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $element_state['values'] collection
 *   for this element. Return nothing to use the default.
 */
function form_type_token_value($element, $input = FALSE) {
  if ($input !== FALSE) {
    return (string) $input;
  }
}

/**
 * Changes submitted form values during form validation.
 *
 * Use this function to change the submitted value of a form element in a form
 * validation function, so that the changed value persists in $form_state
 * through to the submission handlers.
 *
 * Note that form validation functions are specified in the '#validate'
 * component of the form array (the value of $form['#validate'] is an array of
 * validation function names). If the form does not originate in your module,
 * you can implement hook_form_FORM_ID_alter() to add a validation function
 * to $form['#validate'].
 *
 * @param $element
 *   The form element that should have its value updated; in most cases you can
 *   just pass in the element from the $form array, although the only component
 *   that is actually used is '#parents'. If constructing yourself, set
 *   $element['#parents'] to be an array giving the path through the form
 *   array's keys to the element whose value you want to update. For instance,
 *   if you want to update the value of $form['elem1']['elem2'], which should be
 *   stored in $form_state['values']['elem1']['elem2'], you would set
 *   $element['#parents'] = array('elem1','elem2').
 * @param $value
 *   The new value for the form element.
 * @param $form_state
 *   Form state array where the value change should be recorded.
 */
function form_set_value($element, $value, &$form_state) {
  NestedArray::setValue($form_state['values'], $element['#parents'], $value, TRUE);
}

/**
 * Allows PHP array processing of multiple select options with the same value.
 *
 * Used for form select elements which need to validate HTML option groups
 * and multiple options which may return the same value. Associative PHP arrays
 * cannot handle these structures, since they share a common key.
 *
 * @param $array
 *   The form options array to process.
 *
 * @return
 *   An array with all hierarchical elements flattened to a single array.
 */
function form_options_flatten($array) {
  // Always reset static var when first entering the recursion.
  drupal_static_reset('_form_options_flatten');
  return _form_options_flatten($array);
}

/**
 * Iterates over an array and returns a flat array with duplicate keys removed.
 *
 * This function also handles cases where objects are passed as array values.
 */
function _form_options_flatten($array) {
  $return = &drupal_static(__FUNCTION__);

  foreach ($array as $key => $value) {
    if (is_object($value)) {
      _form_options_flatten($value->option);
    }
    elseif (is_array($value)) {
      _form_options_flatten($value);
    }
    else {
      $return[$key] = 1;
    }
  }

  return $return;
}

/**
 * Processes a select list form element.
 *
 * This process callback is mandatory for select fields, since all user agents
 * automatically preselect the first available option of single (non-multiple)
 * select lists.
 *
 * @param $element
 *   The form element to process. Properties used:
 *   - #multiple: (optional) Indicates whether one or more options can be
 *     selected. Defaults to FALSE.
 *   - #default_value: Must be NULL or not set in case there is no value for the
 *     element yet, in which case a first default option is inserted by default.
 *     Whether this first option is a valid option depends on whether the field
 *     is #required or not.
 *   - #required: (optional) Whether the user needs to select an option (TRUE)
 *     or not (FALSE). Defaults to FALSE.
 *   - #empty_option: (optional) The label to show for the first default option.
 *     By default, the label is automatically set to "- Please select -" for a
 *     required field and "- None -" for an optional field.
 *   - #empty_value: (optional) The value for the first default option, which is
 *     used to determine whether the user submitted a value or not.
 *     - If #required is TRUE, this defaults to '' (an empty string).
 *     - If #required is not TRUE and this value isn't set, then no extra option
 *       is added to the select control, leaving the control in a slightly
 *       illogical state, because there's no way for the user to select nothing,
 *       since all user agents automatically preselect the first available
 *       option. But people are used to this being the behavior of select
 *       controls.
 *       @todo Address the above issue in Drupal 8.
 *     - If #required is not TRUE and this value is set (most commonly to an
 *       empty string), then an extra option (see #empty_option above)
 *       representing a "non-selection" is added with this as its value.
 *
 * @see _form_validate()
 */
function form_process_select($element) {
  // #multiple select fields need a special #name.
  if ($element['#multiple']) {
    $element['#attributes']['multiple'] = 'multiple';
    $element['#attributes']['name'] = $element['#name'] . '[]';
  }
  // A non-#multiple select needs special handling to prevent user agents from
  // preselecting the first option without intention. #multiple select lists do
  // not get an empty option, as it would not make sense, user interface-wise.
  else {
    // If the element is set to #required through #states, override the
    // element's #required setting.
    $required = isset($element['#states']['required']) ? TRUE : $element['#required'];
    // If the element is required and there is no #default_value, then add an
    // empty option that will fail validation, so that the user is required to
    // make a choice. Also, if there's a value for #empty_value or
    // #empty_option, then add an option that represents emptiness.
    if (($required && !isset($element['#default_value'])) || isset($element['#empty_value']) || isset($element['#empty_option'])) {
      $element += array(
        '#empty_value' => '',
        '#empty_option' => $required ? t('- Select -') : t('- None -'),
      );
      // The empty option is prepended to #options and purposively not merged
      // to prevent another option in #options mistakenly using the same value
      // as #empty_value.
      $empty_option = array($element['#empty_value'] => $element['#empty_option']);
      $element['#options'] = $empty_option + $element['#options'];
    }
  }
  return $element;
}

/**
 * Returns HTML for a select form element.
 *
 * It is possible to group options together; to do this, change the format of
 * $options to an associative array in which the keys are group labels, and the
 * values are associative arrays in the normal $options format.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #value, #options, #description, #extra,
 *     #multiple, #required, #name, #attributes, #size.
 *
 * @ingroup themeable
 */
function theme_select($variables) {
  $element = $variables['element'];
  element_set_attributes($element, array('id', 'name', 'size'));
  _form_set_attributes($element, array('form-select'));

  return '<select' . new Attribute($element['#attributes']) . '>' . form_select_options($element) . '</select>';
}

/**
 * Converts a select form element's options array into HTML.
 *
 * @param $element
 *   An associative array containing the properties of the element.
 * @param $choices
 *   Mixed: Either an associative array of items to list as choices, or an
 *   object with an 'option' member that is an associative array. This
 *   parameter is only used internally and should not be passed.
 *
 * @return
 *   An HTML string of options for the select form element.
 */
function form_select_options($element, $choices = NULL) {
  if (!isset($choices)) {
    if (empty($element['#options'])) {
      return '';
    }
    $choices = $element['#options'];
  }
  // array_key_exists() accommodates the rare event where $element['#value'] is NULL.
  // isset() fails in this situation.
  $value_valid = isset($element['#value']) || array_key_exists('#value', $element);
  $value_is_array = $value_valid && is_array($element['#value']);
  $options = '';
  foreach ($choices as $key => $choice) {
    if (is_array($choice)) {
      $options .= '<optgroup label="' . $key . '">';
      $options .= form_select_options($element, $choice);
      $options .= '</optgroup>';
    }
    elseif (is_object($choice)) {
      $options .= form_select_options($element, $choice->option);
    }
    else {
      $key = (string) $key;
      if ($value_valid && (!$value_is_array && (string) $element['#value'] === $key || ($value_is_array && in_array($key, $element['#value'])))) {
        $selected = ' selected="selected"';
      }
      else {
        $selected = '';
      }
      $options .= '<option value="' . check_plain($key) . '"' . $selected . '>' . check_plain($choice) . '</option>';
    }
  }
  return $options;
}

/**
 * Returns the indexes of a select element's options matching a given key.
 *
 * This function is useful if you need to modify the options that are
 * already in a form element; for example, to remove choices which are
 * not valid because of additional filters imposed by another module.
 * One example might be altering the choices in a taxonomy selector.
 * To correctly handle the case of a multiple hierarchy taxonomy,
 * #options arrays can now hold an array of objects, instead of a
 * direct mapping of keys to labels, so that multiple choices in the
 * selector can have the same key (and label). This makes it difficult
 * to manipulate directly, which is why this helper function exists.
 *
 * This function does not support optgroups (when the elements of the
 * #options array are themselves arrays), and will return FALSE if
 * arrays are found. The caller must either flatten/restore or
 * manually do their manipulations in this case, since returning the
 * index is not sufficient, and supporting this would make the
 * "helper" too complicated and cumbersome to be of any help.
 *
 * As usual with functions that can return array() or FALSE, do not
 * forget to use === and !== if needed.
 *
 * @param $element
 *   The select element to search.
 * @param $key
 *   The key to look for.
 *
 * @return
 *   An array of indexes that match the given $key. Array will be
 *   empty if no elements were found. FALSE if optgroups were found.
 */
function form_get_options($element, $key) {
  $keys = array();
  foreach ($element['#options'] as $index => $choice) {
    if (is_array($choice)) {
      return FALSE;
    }
    elseif (is_object($choice)) {
      if (isset($choice->option[$key])) {
        $keys[] = $index;
      }
    }
    elseif ($index == $key) {
      $keys[] = $index;
    }
  }
  return $keys;
}

/**
 * Returns HTML for a fieldset form element and its children.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #attributes, #children, #collapsed, #description, #id,
 *     #title, #value.
 *
 * @ingroup themeable
 */
function theme_fieldset($variables) {
  $element = $variables['element'];
  element_set_attributes($element, array('id'));
  _form_set_attributes($element, array('form-wrapper'));

  if (!empty($element['#description'])) {
    $description_id = $element['#attributes']['id'] . '--description';
    $element['#attributes']['aria-describedby'] = $description_id;
  }

  $legend_attributes = array();
  if (isset($element['#title_display']) && $element['#title_display'] == 'invisible') {
    $legend_attributes['class'][] = 'element-invisible';
  }

  $output = '<fieldset' . new Attribute($element['#attributes']) . '>';
  if (!empty($element['#title'])) {
    // Always wrap fieldset legends in a SPAN for CSS positioning.
    $output .= '<legend' . new Attribute($legend_attributes) . '><span class="fieldset-legend">' . $element['#title'] . '</span></legend>';
  }
  $output .= '<div class="fieldset-wrapper">';
  if (!empty($element['#description'])) {
    $attributes = array('class' => 'fieldset-description', 'id' => $description_id);
    $output .= '<div' . new Attribute($attributes) . '>' . $element['#description'] . '</div>';

  }
  $output .= $element['#children'];
  if (isset($element['#value'])) {
    $output .= $element['#value'];
  }
  $output .= '</div>';
  $output .= "</fieldset>\n";
  return $output;
}

/**
 * Returns HTML for a details form element and its children.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #attributes, #children, #collapsed, #description, #id,
 *     #title, #value.
 *
 * @ingroup themeable
 */
function theme_details($variables) {
  $element = $variables['element'];
  element_set_attributes($element, array('id'));
  _form_set_attributes($element, array('form-wrapper'));

  $output = '<details' . new Attribute($element['#attributes']) . '>';
  if (!empty($element['#title'])) {
    $summary_attributes = new Attribute(array(
      'role' => 'button',
    ));
    if (!empty($element['#attributes']['id'])) {
      $summary_attributes['aria-controls'] = $element['#attributes']['id'];
    }
    $summary_attributes['aria-expanded'] = empty($element['#attributes']['open']) ? FALSE : TRUE;
    $summary_attributes['aria-pressed'] = $summary_attributes['aria-expanded'];
    $output .= '<summary' . $summary_attributes . '>' . $element['#title'] . '</summary>';
  }
  $output .= '<div class="details-wrapper">';
  if (!empty($element['#description'])) {
    $output .= '<div class="details-description">' . $element['#description'] . '</div>';
  }
  $output .= $element['#children'];
  if (isset($element['#value'])) {
    $output .= $element['#value'];
  }
  $output .= '</div>';
  $output .= "</details>\n";
  return $output;
}

/**
 * Prepares a #type 'radio' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #required, #return_value, #value, #attributes, #title,
 *   #description.
 *
 * Note: The input "name" attribute needs to be sanitized before output, which
 *       is currently done by initializing Drupal\Core\Template\Attribute with
 *       all the attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_radio($element) {
  $element['#attributes']['type'] = 'radio';
  element_set_attributes($element, array('id', 'name', '#return_value' => 'value'));

  if (isset($element['#return_value']) && $element['#value'] !== FALSE && $element['#value'] == $element['#return_value']) {
    $element['#attributes']['checked'] = 'checked';
  }
  _form_set_attributes($element, array('form-radio'));

  return $element;
}

/**
 * Returns HTML for a set of radio button form elements.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #value, #options, #description, #required,
 *     #attributes, #children.
 *
 * @ingroup themeable
 */
function theme_radios($variables) {
  $element = $variables['element'];
  $attributes = array();
  if (isset($element['#id'])) {
    $attributes['id'] = $element['#id'];
  }
  $attributes['class'] = 'form-radios';
  if (!empty($element['#attributes']['class'])) {
    $attributes['class'] .= ' ' . implode(' ', $element['#attributes']['class']);
  }
  if (isset($element['#attributes']['title'])) {
    $attributes['title'] = $element['#attributes']['title'];
  }
  return '<div' . new Attribute($attributes) . '>' . (!empty($element['#children']) ? $element['#children'] : '') . '</div>';
}

/**
 * Expand a password_confirm field into two text boxes.
 */
function form_process_password_confirm($element) {
  $element['pass1'] =  array(
    '#type' => 'password',
    '#title' => t('Password'),
    '#value' => empty($element['#value']) ? NULL : $element['#value']['pass1'],
    '#required' => $element['#required'],
    '#attributes' => array('class' => array('password-field')),
  );
  $element['pass2'] =  array(
    '#type' => 'password',
    '#title' => t('Confirm password'),
    '#value' => empty($element['#value']) ? NULL : $element['#value']['pass2'],
    '#required' => $element['#required'],
    '#attributes' => array('class' => array('password-confirm')),
  );
  $element['#element_validate'] = array('password_confirm_validate');
  $element['#tree'] = TRUE;

  if (isset($element['#size'])) {
    $element['pass1']['#size'] = $element['pass2']['#size'] = $element['#size'];
  }

  return $element;
}

/**
 * Validates a password_confirm element.
 */
function password_confirm_validate($element, &$element_state) {
  $pass1 = trim($element['pass1']['#value']);
  $pass2 = trim($element['pass2']['#value']);
  if (!empty($pass1) || !empty($pass2)) {
    if (strcmp($pass1, $pass2)) {
      form_error($element, t('The specified passwords do not match.'));
    }
  }
  elseif ($element['#required'] && !empty($element_state['input'])) {
    form_error($element, t('Password field is required.'));
  }

  // Password field must be converted from a two-element array into a single
  // string regardless of validation results.
  form_set_value($element['pass1'], NULL, $element_state);
  form_set_value($element['pass2'], NULL, $element_state);
  form_set_value($element, $pass1, $element_state);

  return $element;

}

/**
 * Returns HTML for an #date form element.
 *
 * Supports HTML5 types of 'date', 'datetime', 'datetime-local', and 'time'.
 * Falls back to a plain textfield. Used as a sub-element by the datetime
 * element type.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #value, #options, #description, #required,
 *     #attributes, #id, #name, #type, #min, #max, #step, #value, #size.
 *
 * @ingroup themeable
 */
function theme_date($variables) {
  $element = $variables['element'];
  if (empty($element['attribute']['type'])) {
    $element['attribute']['type'] = 'date';
  }
  element_set_attributes($element, array('id', 'name', 'type', 'min', 'max', 'step', 'value', 'size'));
  _form_set_attributes($element, array('form-' . $element['attribute']['type']));

  return '<input' . new Attribute($element['#attributes']) . ' />';
}

/**
 * Sets the value for a weight element, with zero as a default.
 */
function weight_value(&$form) {
  if (isset($form['#default_value'])) {
    $form['#value'] = $form['#default_value'];
  }
  else {
    $form['#value'] = 0;
  }
}

/**
 * Expands a radios element into individual radio elements.
 */
function form_process_radios($element) {
  if (count($element['#options']) > 0) {
    $weight = 0;
    foreach ($element['#options'] as $key => $choice) {
      // Maintain order of options as defined in #options, in case the element
      // defines custom option sub-elements, but does not define all option
      // sub-elements.
      $weight += 0.001;

      $element += array($key => array());
      // Generate the parents as the autogenerator does, so we will have a
      // unique id for each radio button.
      $parents_for_id = array_merge($element['#parents'], array($key));
      $element[$key] += array(
        '#type' => 'radio',
        '#title' => $choice,
        // The key is sanitized in Drupal\Core\Template\Attribute during output
        // from the theme function.
        '#return_value' => $key,
        // Use default or FALSE. A value of FALSE means that the radio button is
        // not 'checked'.
        '#default_value' => isset($element['#default_value']) ? $element['#default_value'] : FALSE,
        '#attributes' => $element['#attributes'],
        '#parents' => $element['#parents'],
        '#id' => drupal_html_id('edit-' . implode('-', $parents_for_id)),
        '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
        '#weight' => $weight,
      );
    }
  }
  return $element;
}

/**
 * Prepares a #type 'checkbox' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #return_value, #description, #required,
 *   #attributes, #checked.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_checkbox($element) {
  $element['#attributes']['type'] = 'checkbox';
  element_set_attributes($element, array('id', 'name', '#return_value' => 'value'));

  // Unchecked checkbox has #value of integer 0.
  if (!empty($element['#checked'])) {
    $element['#attributes']['checked'] = 'checked';
  }
  _form_set_attributes($element, array('form-checkbox'));

  return $element;
}

/**
 * Returns HTML for a set of checkbox form elements.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #children, #attributes.
 *
 * @ingroup themeable
 */
function theme_checkboxes($variables) {
  $element = $variables['element'];
  $attributes = array();
  if (isset($element['#id'])) {
    $attributes['id'] = $element['#id'];
  }
  $attributes['class'][] = 'form-checkboxes';
  if (!empty($element['#attributes']['class'])) {
    $attributes['class'] = array_merge($attributes['class'], $element['#attributes']['class']);
  }
  if (isset($element['#attributes']['title'])) {
    $attributes['title'] = $element['#attributes']['title'];
  }
  return '<div' . new Attribute($attributes) . '>' . (!empty($element['#children']) ? $element['#children'] : '') . '</div>';
}

/**
 * Adds form element theming to an element if its title or description is set.
 *
 * This is used as a pre render function for checkboxes and radios.
 */
function form_pre_render_conditional_form_element($element) {
  $t = get_t();
  // Set the element's title attribute to show #title as a tooltip, if needed.
  if (isset($element['#title']) && $element['#title_display'] == 'attribute') {
    $element['#attributes']['title'] = $element['#title'];
    if (!empty($element['#required'])) {
      // Append an indication that this field is required.
      $element['#attributes']['title'] .= ' (' . $t('Required') . ')';
    }
  }

  if (isset($element['#title']) || isset($element['#description'])) {
    $element['#theme_wrappers'][] = 'form_element';
  }
  return $element;
}

/**
 * Processes a form button element.
 */
function form_process_button($element, $form_state) {
  // If this is a button intentionally allowing incomplete form submission
  // (e.g., a "Previous" or "Add another item" button), then also skip
  // client-side validation.
  if (isset($element['#limit_validation_errors']) && $element['#limit_validation_errors'] !== FALSE) {
    $element['#attributes']['formnovalidate'] = 'formnovalidate';
  }
  return $element;
}

/**
 * Sets the #checked property of a checkbox element.
 */
function form_process_checkbox($element, $form_state) {
  $value = $element['#value'];
  $return_value = $element['#return_value'];
  // On form submission, the #value of an available and enabled checked
  // checkbox is #return_value, and the #value of an available and enabled
  // unchecked checkbox is integer 0. On not submitted forms, and for
  // checkboxes with #access=FALSE or #disabled=TRUE, the #value is
  // #default_value (integer 0 if #default_value is NULL). Most of the time,
  // a string comparison of #value and #return_value is sufficient for
  // determining the "checked" state, but a value of TRUE always means checked
  // (even if #return_value is 'foo'), and a value of FALSE or integer 0 always
  // means unchecked (even if #return_value is '' or '0').
  if ($value === TRUE || $value === FALSE || $value === 0) {
    $element['#checked'] = (bool) $value;
  }
  else {
    // Compare as strings, so that 15 is not considered equal to '15foo', but 1
    // is considered equal to '1'. This cast does not imply that either #value
    // or #return_value is expected to be a string.
    $element['#checked'] = ((string) $value === (string) $return_value);
  }
  return $element;
}

/**
 * Processes a checkboxes form element.
 */
function form_process_checkboxes($element) {
  $value = is_array($element['#value']) ? $element['#value'] : array();
  $element['#tree'] = TRUE;
  if (count($element['#options']) > 0) {
    if (!isset($element['#default_value']) || $element['#default_value'] == 0) {
      $element['#default_value'] = array();
    }
    $weight = 0;
    foreach ($element['#options'] as $key => $choice) {
      // Integer 0 is not a valid #return_value, so use '0' instead.
      // @see form_type_checkbox_value().
      // @todo For Drupal 8, cast all integer keys to strings for consistency
      //   with form_process_radios().
      if ($key === 0) {
        $key = '0';
      }
      // Maintain order of options as defined in #options, in case the element
      // defines custom option sub-elements, but does not define all option
      // sub-elements.
      $weight += 0.001;

      $element += array($key => array());
      $element[$key] += array(
        '#type' => 'checkbox',
        '#title' => $choice,
        '#return_value' => $key,
        '#default_value' => isset($value[$key]) ? $key : NULL,
        '#attributes' => $element['#attributes'],
        '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
        '#weight' => $weight,
      );
    }
  }
  return $element;
}

/**
 * Processes a form actions container element.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   form actions container.
 * @param $form_state
 *   The $form_state array for the form this element belongs to.
 *
 * @return
 *   The processed element.
 */
function form_process_actions($element, &$form_state) {
  $element['#attributes']['class'][] = 'form-actions';
  return $element;
}

/**
 * #pre_render callback for #type 'actions'.
 *
 * This callback iterates over all child elements of the #type 'actions'
 * container to look for elements with a #dropbutton property, so as to group
 * those elements into dropbuttons. As such, it works similar to #group, but is
 * specialized for dropbuttons.
 *
 * The value of #dropbutton denotes the dropbutton to group the child element
 * into. For example, two different values of 'foo' and 'bar' on child elements
 * would generate two separate dropbuttons, which each contain the corresponding
 * buttons.
 *
 * @param array $element
 *   The #type 'actions' element to process.
 *
 * @return array
 *   The processed #type 'actions' element, including individual buttons grouped
 *   into new #type 'dropbutton' elements.
 */
function form_pre_render_actions_dropbutton(array $element) {
  $dropbuttons = array();
  foreach (element_children($element, TRUE) as $key) {
    if (isset($element[$key]['#dropbutton'])) {
      $dropbutton = $element[$key]['#dropbutton'];
      // If there is no dropbutton for this button group yet, create one.
      if (!isset($dropbuttons[$dropbutton])) {
        $dropbuttons[$dropbutton] = array(
          '#type' => 'dropbutton',
        );
      }
      // Add this button to the corresponding dropbutton.
      // @todo Change #type 'dropbutton' to be based on theme_item_list()
      //   instead of theme_links() to avoid this preemptive rendering.
      $button = drupal_render($element[$key]);
      $dropbuttons[$dropbutton]['#links'][$key] = array(
        'title' => $button,
        'html' => TRUE,
      );
    }
  }
  // @todo For now, all dropbuttons appear first. Consider to invent a more
  //   fancy sorting/injection algorithm here.
  return $dropbuttons + $element;
}

/**
 * #process callback for #pattern form element property.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   generic input element.
 * @param $form_state
 *   The $form_state array for the form this element belongs to.
 *
 * @return
 *   The processed element.
 *
 * @see form_validate_pattern()
 */
function form_process_pattern($element, &$form_state) {
  if (isset($element['#pattern']) && !isset($element['#attributes']['pattern'])) {
    $element['#attributes']['pattern'] = $element['#pattern'];
    $element['#element_validate'][] = 'form_validate_pattern';
  }

  return $element;
}

/**
 * #element_validate callback for #pattern form element property.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   generic form element.
 * @param $form_state
 *   The $form_state array for the form this element belongs to.
 *
 * @see form_process_pattern()
 */
function form_validate_pattern($element, &$form_state) {
  if ($element['#value'] !== '') {
    // The pattern must match the entire string and should have the same
    // behavior as the RegExp object in ECMA 262.
    // - Use bracket-style delimiters to avoid introducing a special delimiter
    //   character like '/' that would have to be escaped.
    // - Put in brackets so that the pattern can't interfere with what's
    //   prepended and appended.
    $pattern = '{^(?:' . $element['#pattern'] . ')$}';

    if (!preg_match($pattern, $element['#value'])) {
      form_error($element, t('%name field is not in the right format.', array('%name' => $element['#title'])));
    }
  }
}

/**
 * Processes a container element.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   container.
 * @param $form_state
 *   The $form_state array for the form this element belongs to.
 *
 * @return
 *   The processed element.
 */
function form_process_container($element, &$form_state) {
  // Generate the ID of the element if it's not explicitly given.
  if (!isset($element['#id'])) {
    $element['#id'] = drupal_html_id(implode('-', $element['#parents']) . '-wrapper');
  }
  return $element;
}

/**
 * Returns HTML to wrap child elements in a container.
 *
 * Used for grouped form items. Can also be used as a #theme_wrapper for any
 * renderable element, to surround it with a <div> and add attributes such as
 * classes or an HTML id.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #id, #attributes, #children.
 *
 * @ingroup themeable
 */
function theme_container($variables) {
  $element = $variables['element'];

  // Special handling for form elements.
  if (isset($element['#array_parents'])) {
    // Assign an html ID.
    if (!isset($element['#attributes']['id'])) {
      $element['#attributes']['id'] = $element['#id'];
    }
    // Add the 'form-wrapper' class.
    $element['#attributes']['class'][] = 'form-wrapper';
  }

  return '<div' . new Attribute($element['#attributes']) . '>' . $element['#children'] . '</div>';
}

/**
 * Returns HTML for a table with radio buttons or checkboxes.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties and children of
 *     the tableselect element. Properties used: #header, #options, #empty,
 *     and #js_select. The #options property is an array of selection options;
 *     each array element of #options is an array of properties. These
 *     properties can include #attributes, which is added to the
 *     table row's HTML attributes; see theme_table(). An example of per-row
 *     options:
 *     @code
 *     $options = array(
 *       array(
 *         'title' => 'How to Learn Drupal',
 *         'content_type' => 'Article',
 *         'status' => 'published',
 *         '#attributes' => array('class' => array('article-row')),
 *       ),
 *       array(
 *         'title' => 'Privacy Policy',
 *         'content_type' => 'Page',
 *         'status' => 'published',
 *         '#attributes' => array('class' => array('page-row')),
 *       ),
 *     );
 *     $header = array(
 *       'title' => t('Title'),
 *       'content_type' => t('Content type'),
 *       'status' => t('Status'),
 *     );
 *     $form['table'] = array(
 *       '#type' => 'tableselect',
 *       '#header' => $header,
 *       '#options' => $options,
 *       '#empty' => t('No content available.'),
 *     );
 *     @endcode
 *
 * @ingroup themeable
 */
function theme_tableselect($variables) {
  $element = $variables['element'];
  $rows = array();
  $header = $element['#header'];
  if (!empty($element['#options'])) {
    // Generate a table row for each selectable item in #options.
    foreach (element_children($element) as $key) {
      $row = array();

      $row['data'] = array();
      if (isset($element['#options'][$key]['#attributes'])) {
        $row += $element['#options'][$key]['#attributes'];
      }
      // Render the checkbox / radio element.
      $row['data'][] = drupal_render($element[$key]);

      // As theme_table only maps header and row columns by order, create the
      // correct order by iterating over the header fields.
      foreach ($element['#header'] as $fieldname => $title) {
        // A row cell can span over multiple headers, which means less row cells
        // than headers could be present.
        if (isset($element['#options'][$key][$fieldname])) {
          // A header can span over multiple cells and in this case the cells
          // are passed in an array. The order of this array determines the
          // order in which they are added.
          if (!isset($element['#options'][$key][$fieldname]['data']) && is_array($element['#options'][$key][$fieldname])) {
            foreach ($element['#options'][$key][$fieldname] as $cell) {
              $row['data'][] = $cell;
            }
          }
          else {
            $row['data'][] = $element['#options'][$key][$fieldname];
          }
        }
      }
      $rows[] = $row;
    }
    // Add an empty header or a "Select all" checkbox to provide room for the
    // checkboxes/radios in the first table column.
    if ($element['#js_select']) {
      // Add a "Select all" checkbox.
      drupal_add_library('system', 'drupal.tableselect');
      array_unshift($header, array('class' => array('select-all')));
    }
    else {
      // Add an empty header when radio buttons are displayed or a "Select all"
      // checkbox is not desired.
      array_unshift($header, '');
    }
  }
  return theme('table', array('header' => $header, 'rows' => $rows, 'empty' => $element['#empty'], 'attributes' => $element['#attributes']));
}

/**
 * Creates checkbox or radio elements to populate a tableselect table.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   tableselect element.
 *
 * @return
 *   The processed element.
 */
function form_process_tableselect($element) {

  if ($element['#multiple']) {
    $value = is_array($element['#value']) ? $element['#value'] : array();
  }
  else {
    // Advanced selection behavior makes no sense for radios.
    $element['#js_select'] = FALSE;
  }

  $element['#tree'] = TRUE;

  if (count($element['#options']) > 0) {
    if (!isset($element['#default_value']) || $element['#default_value'] === 0) {
      $element['#default_value'] = array();
    }

    // Create a checkbox or radio for each item in #options in such a way that
    // the value of the tableselect element behaves as if it had been of type
    // checkboxes or radios.
    foreach ($element['#options'] as $key => $choice) {
      // Do not overwrite manually created children.
      if (!isset($element[$key])) {
        if ($element['#multiple']) {
          $title = '';
          if (!empty($element['#options'][$key]['title']['data']['#title'])) {
            $title = t('Update @title', array(
              '@title' => $element['#options'][$key]['title']['data']['#title'],
            ));
          }
          $element[$key] = array(
            '#type' => 'checkbox',
            '#title' => $title,
            '#title_display' => 'invisible',
            '#return_value' => $key,
            '#default_value' => isset($value[$key]) ? $key : NULL,
            '#attributes' => $element['#attributes'],
          );
        }
        else {
          // Generate the parents as the autogenerator does, so we will have a
          // unique id for each radio button.
          $parents_for_id = array_merge($element['#parents'], array($key));
          $element[$key] = array(
            '#type' => 'radio',
            '#title' => '',
            '#return_value' => $key,
            '#default_value' => ($element['#default_value'] == $key) ? $key : NULL,
            '#attributes' => $element['#attributes'],
            '#parents' => $element['#parents'],
            '#id' => drupal_html_id('edit-' . implode('-', $parents_for_id)),
            '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
          );
        }
        if (isset($element['#options'][$key]['#weight'])) {
          $element[$key]['#weight'] = $element['#options'][$key]['#weight'];
        }
      }
    }
  }
  else {
    $element['#value'] = array();
  }
  return $element;
}

/**
 * #process callback for #type 'table' to add tableselect support.
 *
 * @param array $element
 *   An associative array containing the properties and children of the
 *   table element.
 * @param array $form_state
 *   The current state of the form.
 *
 * @return array
 *   The processed element.
 *
 * @see form_process_tableselect()
 * @see theme_tableselect()
 */
function form_process_table($element, &$form_state) {
  if ($element['#tableselect']) {
    if ($element['#multiple']) {
      $value = is_array($element['#value']) ? $element['#value'] : array();
    }
    // Advanced selection behaviour makes no sense for radios.
    else {
      $element['#js_select'] = FALSE;
    }
    // Add a "Select all" checkbox column to the header.
    // @todo D8: Rename into #select_all?
    if ($element['#js_select']) {
      $element['#attached']['library'][] = array('system', 'drupal.tableselect');
      array_unshift($element['#header'], array('class' => array('select-all')));
    }
    // Add an empty header column for radio buttons or when a "Select all"
    // checkbox is not desired.
    else {
      array_unshift($element['#header'], '');
    }

    if (!isset($element['#default_value']) || $element['#default_value'] === 0) {
      $element['#default_value'] = array();
    }
    // Create a checkbox or radio for each row in a way that the value of the
    // tableselect element behaves as if it had been of #type checkboxes or
    // radios.
    foreach (element_children($element) as $key) {
      // Do not overwrite manually created children.
      if (!isset($element[$key]['select'])) {
        // Determine option label; either an assumed 'title' column, or the
        // first available column containing a #title or #markup.
        // @todo Consider to add an optional $element[$key]['#title_key']
        //   defaulting to 'title'?
        $title = '';
        if (!empty($element[$key]['title']['#title'])) {
          $title = $element[$key]['title']['#title'];
        }
        else {
          foreach (element_children($element[$key]) as $column) {
            if (isset($element[$key][$column]['#title'])) {
              $title = $element[$key][$column]['#title'];
              break;
            }
            if (isset($element[$key][$column]['#markup'])) {
              $title = $element[$key][$column]['#markup'];
              break;
            }
          }
        }
        if ($title !== '') {
          $title = t('Update !title', array('!title' => $title));
        }

        // Prepend the select column to existing columns.
        $element[$key] = array('select' => array()) + $element[$key];
        $element[$key]['select'] += array(
          '#type' => $element['#multiple'] ? 'checkbox' : 'radio',
          '#title' => $title,
          '#title_display' => 'invisible',
          // @todo If rows happen to use numeric indexes instead of string keys,
          //   this results in a first row with $key === 0, which is always FALSE.
          '#return_value' => $key,
          '#attributes' => $element['#attributes'],
        );
        $element_parents = array_merge($element['#parents'], array($key));
        if ($element['#multiple']) {
          $element[$key]['select']['#default_value'] = isset($value[$key]) ? $key : NULL;
          $element[$key]['select']['#parents'] = $element_parents;
        }
        else {
          $element[$key]['select']['#default_value'] = ($element['#default_value'] == $key ? $key : NULL);
          $element[$key]['select']['#parents'] = $element['#parents'];
          $element[$key]['select']['#id'] = drupal_html_id('edit-' . implode('-', $element_parents));
        }
      }
    }
  }

  return $element;
}

/**
 * #element_validate callback for #type 'table'.
 *
 * @param array $element
 *   An associative array containing the properties and children of the
 *   table element.
 * @param array $form_state
 *   The current state of the form.
 */
function form_validate_table($element, &$form_state) {
  // Skip this validation if the button to submit the form does not require
  // selected table row data.
  if (empty($form_state['triggering_element']['#tableselect'])) {
    return;
  }
  if ($element['#multiple']) {
    if (!is_array($element['#value']) || !count(array_filter($element['#value']))) {
      form_error($element, t('No items selected.'));
    }
  }
  elseif (!isset($element['#value']) || $element['#value'] === '') {
    form_error($element, t('No item selected.'));
  }
}

/**
 * Processes a machine-readable name form element.
 *
 * @param $element
 *   The form element to process. Properties used:
 *   - #machine_name: An associative array containing:
 *     - exists: A function name to invoke for checking whether a submitted
 *       machine name value already exists. The submitted value is passed as
 *       argument. In most cases, an existing API or menu argument loader
 *       function can be re-used. The callback is only invoked, if the submitted
 *       value differs from the element's #default_value.
 *     - source: (optional) The #array_parents of the form element containing
 *       the human-readable name (i.e., as contained in the $form structure) to
 *       use as source for the machine name. Defaults to array('label').
 *     - label: (optional) A text to display as label for the machine name value
 *       after the human-readable name form element. Defaults to "Machine name".
 *     - replace_pattern: (optional) A regular expression (without delimiters)
 *       matching disallowed characters in the machine name. Defaults to
 *       '[^a-z0-9_]+'.
 *     - replace: (optional) A character to replace disallowed characters in the
 *       machine name via JavaScript. Defaults to '_' (underscore). When using a
 *       different character, 'replace_pattern' needs to be set accordingly.
 *     - error: (optional) A custom form error message string to show, if the
 *       machine name contains disallowed characters.
 *     - standalone: (optional) Whether the live preview should stay in its own
 *       form element rather than in the suffix of the source element. Defaults
 *       to FALSE.
 *   - #maxlength: (optional) Should be set to the maximum allowed length of the
 *     machine name. Defaults to 64.
 *   - #disabled: (optional) Should be set to TRUE in case an existing machine
 *     name must not be changed after initial creation.
 */
function form_process_machine_name($element, &$form_state) {
  // We need to pass the langcode to the client.
  $language = language(LANGUAGE_TYPE_INTERFACE);

  // Apply default form element properties.
  $element += array(
    '#title' => t('Machine-readable name'),
    '#description' => t('A unique machine-readable name. Can only contain lowercase letters, numbers, and underscores.'),
    '#machine_name' => array(),
    '#field_prefix' => '',
    '#field_suffix' => '',
    '#suffix' => '',
  );
  // A form element that only wants to set one #machine_name property (usually
  // 'source' only) would leave all other properties undefined, if the defaults
  // were defined in hook_element_info(). Therefore, we apply the defaults here.
  $element['#machine_name'] += array(
    'source' => array('label'),
    'target' => '#' . $element['#id'],
    'label' => t('Machine name'),
    'replace_pattern' => '[^a-z0-9_]+',
    'replace' => '_',
    'standalone' => FALSE,
    'field_prefix' => $element['#field_prefix'],
    'field_suffix' => $element['#field_suffix'],
  );

  // By default, machine names are restricted to Latin alphanumeric characters.
  // So, default to LTR directionality.
  if (!isset($element['#attributes'])) {
    $element['#attributes'] = array();
  }
  $element['#attributes'] += array('dir' => 'ltr');

  // The source element defaults to array('name'), but may have been overidden.
  if (empty($element['#machine_name']['source'])) {
    return $element;
  }

  // Retrieve the form element containing the human-readable name from the
  // complete form in $form_state. By reference, because we may need to append
  // a #field_suffix that will hold the live preview.
  $key_exists = NULL;
  $source = NestedArray::getValue($form_state['complete_form'], $element['#machine_name']['source'], $key_exists);
  if (!$key_exists) {
    return $element;
  }

  $suffix_id = $source['#id'] . '-machine-name-suffix';
  $element['#machine_name']['suffix'] = '#' . $suffix_id;

  if ($element['#machine_name']['standalone']) {
    $element['#suffix'] .= ' <small id="' . $suffix_id . '">&nbsp;</small>';
  }
  else {
    // Append a field suffix to the source form element, which will contain
    // the live preview of the machine name.
    $source += array('#field_suffix' => '');
    $source['#field_suffix'] .= ' <small id="' . $suffix_id . '">&nbsp;</small>';

    $parents = array_merge($element['#machine_name']['source'], array('#field_suffix'));
    NestedArray::setValue($form_state['complete_form'], $parents, $source['#field_suffix']);
  }

  $js_settings = array(
    'type' => 'setting',
    'data' => array(
      'machineName' => array(
        '#' . $source['#id'] => $element['#machine_name'],
      ),
      'langcode' => $language->langcode,
    ),
  );
  $element['#attached']['library'][] = array('system', 'drupal.machine-name');
  $element['#attached']['js'][] = $js_settings;

  return $element;
}

/**
 * Form element validation handler for machine_name elements.
 *
 * Note that #maxlength is validated by _form_validate() already.
 */
function form_validate_machine_name(&$element, &$form_state) {
  // Verify that the machine name not only consists of replacement tokens.
  if (preg_match('@^' . $element['#machine_name']['replace'] . '+$@', $element['#value'])) {
    form_error($element, t('The machine-readable name must contain unique characters.'));
  }

  // Verify that the machine name contains no disallowed characters.
  if (preg_match('@' . $element['#machine_name']['replace_pattern'] . '@', $element['#value'])) {
    if (!isset($element['#machine_name']['error'])) {
      // Since a hyphen is the most common alternative replacement character,
      // a corresponding validation error message is supported here.
      if ($element['#machine_name']['replace'] == '-') {
        form_error($element, t('The machine-readable name must contain only lowercase letters, numbers, and hyphens.'));
      }
      // Otherwise, we assume the default (underscore).
      else {
        form_error($element, t('The machine-readable name must contain only lowercase letters, numbers, and underscores.'));
      }
    }
    else {
      form_error($element, $element['#machine_name']['error']);
    }
  }

  // Verify that the machine name is unique.
  if ($element['#default_value'] !== $element['#value']) {
    $function = $element['#machine_name']['exists'];
    if ($function($element['#value'], $element, $form_state)) {
      form_error($element, t('The machine-readable name is already in use. It must be unique.'));
    }
  }
}

/**
 * Arranges elements into groups.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   element. Note that $element must be taken by reference here, so processed
 *   child elements are taken over into $form_state.
 * @param $form_state
 *   The $form_state array for the form this element belongs to.
 *
 * @return
 *   The processed element.
 */
function form_process_group(&$element, &$form_state) {
  $parents = implode('][', $element['#parents']);

  // Each details element forms a new group. The #type 'vertical_tabs' basically
  // only injects a new details element.
  $form_state['groups'][$parents]['#group_exists'] = TRUE;
  $element['#groups'] = &$form_state['groups'];

  // Process vertical tabs group member details elements.
  if (isset($element['#group'])) {
    // Add this details element to the defined group (by reference).
    $group = $element['#group'];
    $form_state['groups'][$group][] = &$element;
  }

  // Contains form element summary functionalities.
  $element['#attached']['library'][] = array('system', 'drupal.form');

  return $element;
}

/**
 * Adds form element theming to details.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   details.
 *
 * @return
 *   The modified element.
 */
function form_pre_render_details($element) {
  // The .form-wrapper class is required for #states to treat details like
  // containers.
  if (!isset($element['#attributes']['class'])) {
    $element['#attributes']['class'] = array();
  }

  // Collapsible details.
  $element['#attached']['library'][] = array('system', 'drupal.collapse');
  if (empty($element['#collapsed'])) {
    $element['#attributes']['open'] = 'open';
  }

  return $element;
}

/**
 * Adds members of this group as actual elements for rendering.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   element.
 *
 * @return
 *   The modified element with all group members.
 */
function form_pre_render_group($element) {
  // The element may be rendered outside of a Form API context.
  if (!isset($element['#parents']) || !isset($element['#groups'])) {
    return $element;
  }

  // Inject group member elements belonging to this group.
  $parents = implode('][', $element['#parents']);
  $children = element_children($element['#groups'][$parents]);
  if (!empty($children)) {
    foreach ($children as $key) {
      // Break references and indicate that the element should be rendered as
      // group member.
      $child = (array) $element['#groups'][$parents][$key];
      $child['#group_details'] = TRUE;
      // Inject the element as new child element.
      $element[] = $child;

      $sort = TRUE;
    }
    // Re-sort the element's children if we injected group member elements.
    if (isset($sort)) {
      $element['#sorted'] = FALSE;
    }
  }

  if (isset($element['#group'])) {
    $group = $element['#group'];
    // If this element belongs to a group, but the group-holding element does
    // not exist, we need to render it (at its original location).
    if (!isset($element['#groups'][$group]['#group_exists'])) {
      // Intentionally empty to clarify the flow; we simply return $element.
    }
    // If we injected this element into the group, then we want to render it.
    elseif (!empty($element['#group_details'])) {
      // Intentionally empty to clarify the flow; we simply return $element.
    }
    // Otherwise, this element belongs to a group and the group exists, so we do
    // not render it.
    elseif (element_children($element['#groups'][$group])) {
      $element['#printed'] = TRUE;
    }
  }

  return $element;
}

/**
 * Creates a group formatted as vertical tabs.
 *
 * @param $element
 *   An associative array containing the properties and children of the
 *   details element.
 * @param $form_state
 *   The $form_state array for the form this vertical tab widget belongs to.
 *
 * @return
 *   The processed element.
 */
function form_process_vertical_tabs($element, &$form_state) {
  // Inject a new details as child, so that form_process_details() processes
  // this details element like any other details.
  $element['group'] = array(
    '#type' => 'details',
    '#theme_wrappers' => array(),
    '#parents' => $element['#parents'],
  );

  // Add an invisible label for accessibility.
  if (!isset($element['#title'])) {
    $element['#title'] = t('Vertical Tabs');
    $element['#title_display'] = 'invisible';
  }

  $element['#attached']['library'][] = array('system', 'drupal.vertical-tabs');

  // The JavaScript stores the currently selected tab in this hidden
  // field so that the active tab can be restored the next time the
  // form is rendered, e.g. on preview pages or when form validation
  // fails.
  $name = implode('__', $element['#parents']);
  if (isset($form_state['values'][$name . '__active_tab'])) {
    $element['#default_tab'] = $form_state['values'][$name . '__active_tab'];
  }
  $element[$name . '__active_tab'] = array(
    '#type' => 'hidden',
    '#default_value' => $element['#default_tab'],
    '#attributes' => array('class' => array('vertical-tabs-active-tab')),
  );

  return $element;
}

/**
 * Prepares a vertical_tabs element for rendering.
 *
 * @param array $element
 *   An associative array containing the properties and children of the
 *   vertical tabs element.
 *
 * @return array
 *   The modified element.
 */
function form_pre_render_vertical_tabs($element) {
  // Do not render the vertical tabs element if it is empty.
  $group = implode('][', $element['#parents']);
  if (!element_get_visible_children($element['group']['#groups'][$group])) {
    $element['#printed'] = TRUE;
  }
  return $element;
}

/**
 * Returns HTML for an element's children details as vertical tabs.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties and children of
 *     the details element. Properties used: #children.
 *
 * @ingroup themeable
 */
function theme_vertical_tabs($variables) {
  $element = $variables['element'];
  return '<div class="vertical-tabs-panes">' . $element['#children'] . '</div>';
}

/**
 * Adds autocomplete functionality to elements with a valid #autocomplete_path.
 *
 * Suppose your autocomplete path in the menu system is 'mymodule_autocomplete.'
 * In your form you have:
 * @code
 * '#autocomplete_path' => 'mymodule_autocomplete/' . $some_key . '/' . $some_id,
 * @endcode
 * The user types in "keywords" so the full path called is:
 * 'mymodule_autocomplete/$some_key/$some_id?q=keywords'
 *
 * @param $element
 *   The form element to process. Properties used:
 *   - #autocomplete_path: A system path to be used as callback URL by the
 *     autocomplete JavaScript library.
 */
function form_process_autocomplete($element, &$form_state) {
  if (!empty($element['#autocomplete_path']) && drupal_valid_path($element['#autocomplete_path'])) {
    $element['#attributes']['class'][] = 'form-autocomplete';
    $element['#attached']['library'][] = array('system', 'drupal.autocomplete');
    // Provide a hidden element for the JavaScript behavior to bind to. Since
    // this element is for client-side functionality only, do not process input.
    // @todo Refactor autocomplete.js to accept Drupal.settings instead of
    //   requiring extraneous markup.
    $element['autocomplete'] = array(
      '#type' => 'hidden',
      '#input' => FALSE,
      '#value' => url($element['#autocomplete_path'], array('absolute' => TRUE)),
      '#disabled' => TRUE,
      '#attributes' => array(
        'class' => array('autocomplete'),
        'id' => $element['#id'] . '-autocomplete',
      ),
    );
  }
  return $element;
}

/**
 * Preprocesses variables for theme_input().
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *
 * @ingroup themeable
 */
function template_preprocess_input(&$variables) {
  $element = $variables['element'];
  $variables['attributes'] = new Attribute($element['#attributes']);
}

/**
 * Returns HTML for an input form element.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #attributes.
 *
 * @ingroup themeable
 */
function theme_input($variables) {
  $element = $variables['element'];
  $attributes = $variables['attributes'];
  return '<input' . $attributes . ' />' . drupal_render_children($element);
}

/**
 * Prepares a #type 'button' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #attributes, #button_type, #name, #value.
 *
 * The #button_type property accepts any value, though core themes have CSS that
 * styles the following button_types appropriately: 'primary', 'danger'.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_button($element) {
  $element['#attributes']['type'] = 'submit';
  element_set_attributes($element, array('id', 'name', 'value'));

  $element['#attributes']['class'][] = 'button';
  if (!empty($element['#button_type'])) {
    $element['#attributes']['class'][] = 'button-' . $element['#button_type'];
  }
  // @todo Various JavaScript depends on this button class.
  $element['#attributes']['class'][] = 'form-submit';

  if (!empty($element['#attributes']['disabled'])) {
    $element['#attributes']['class'][] = 'form-button-disabled';
  }

  return $element;
}

/**
 * Prepares a #type 'image_button' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #attributes, #button_type, #name, #value, #title, #src.
 *
 * The #button_type property accepts any value, though core themes have css that
 * styles the following button_types appropriately: 'primary', 'danger'.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_image_button($element) {
  $element['#attributes']['type'] = 'image';
  element_set_attributes($element, array('id', 'name', 'value'));

  $element['#attributes']['src'] = file_create_url($element['#src']);
  if (!empty($element['#title'])) {
    $element['#attributes']['alt'] = $element['#title'];
    $element['#attributes']['title'] = $element['#title'];
  }

  $element['#attributes']['class'][] = 'image-button';
  if (!empty($element['#button_type'])) {
    $element['#attributes']['class'][] = 'image-button-' . $element['#button_type'];
  }
  // @todo Various JavaScript depends on this button class.
  $element['#attributes']['class'][] = 'form-submit';

  if (!empty($element['#attributes']['disabled'])) {
    $element['#attributes']['class'][] = 'image-button-disabled';
  }

  return $element;
}

/**
 * Prepares a #type 'hidden' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #name, #value, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_hidden($element) {
  $element['#attributes']['type'] = 'hidden';
  element_set_attributes($element, array('name', 'value'));

  return $element;
}

/**
 * Prepares a #type 'textfield' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_textfield($element) {
  $element['#attributes']['type'] = 'text';
  element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-text'));

  return $element;
}

/**
 * Prepares a #type 'email' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_email($element) {
  $element['#attributes']['type'] = 'email';
  element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-email'));

  return $element;
}

/**
 * Form element validation handler for #type 'email'.
 *
 * Note that #maxlength and #required is validated by _form_validate() already.
 */
function form_validate_email(&$element, &$form_state) {
  $value = trim($element['#value']);
  form_set_value($element, $value, $form_state);

  if ($value !== '' && !valid_email_address($value)) {
    form_error($element, t('The e-mail address %mail is not valid.', array('%mail' => $value)));
  }
}

/**
 * Prepares a #type 'tel' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_tel($element) {
  $element['#attributes']['type'] = 'tel';
  element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-tel'));

  return $element;
}

/**
 * Prepares a #type 'number' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #min, #max, #placeholder,
 *   #required, #attributes, #step.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_number($element) {
  $element['#attributes']['type'] = 'number';
  element_set_attributes($element, array('id', 'name', 'value', 'step', 'min', 'max', 'placeholder'));
  _form_set_attributes($element, array('form-number'));

  return $element;
}

/**
 * Prepares a #type 'range' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #min, #max, #attributes,
 *   #step.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_range($element) {
  $element['#attributes']['type'] = 'range';
  element_set_attributes($element, array('id', 'name', 'value', 'step', 'min', 'max'));
  _form_set_attributes($element, array('form-range'));

  return $element;
}

/**
 * Form element validation handler for #type 'number'.
 *
 * Note that #required is validated by _form_validate() already.
 */
function form_validate_number(&$element, &$form_state) {
  $value = $element['#value'];
  if ($value === '') {
    return;
  }

  $name = empty($element['#title']) ? $element['#parents'][0] : $element['#title'];

  // Ensure the input is numeric.
  if (!is_numeric($value)) {
    form_error($element, t('%name must be a number.', array('%name' => $name)));
    return;
  }

  // Ensure that the input is greater than the #min property, if set.
  if (isset($element['#min']) && $value < $element['#min']) {
    form_error($element, t('%name must be higher or equal to %min.', array('%name' => $name, '%min' => $element['#min'])));
  }

  // Ensure that the input is less than the #max property, if set.
  if (isset($element['#max']) && $value > $element['#max']) {
    form_error($element, t('%name must be below or equal to %max.', array('%name' => $name, '%max' => $element['#max'])));
  }

  if (isset($element['#step']) && strtolower($element['#step']) != 'any') {
    // Check that the input is an allowed multiple of #step (offset by #min if
    // #min is set).
    $offset = isset($element['#min']) ? $element['#min'] : 0.0;

    if (!valid_number_step($value, $element['#step'], $offset)) {
      form_error($element, t('%name is not a valid number.', array('%name' => $name)));
    }
  }
}

/**
 * Determines the value for a range element.
 *
 * Make sure range elements always have a value. The 'required' attribute is not
 * allowed for range elements.
 *
 * @param $element
 *   The form element whose value is being populated.
 * @param $input
 *   The incoming input to populate the form element. If this is FALSE, the
 *   element's default value should be returned.
 *
 * @return
 *   The data that will appear in the $form_state['values'] collection for
 *   this element. Return nothing to use the default.
 */
function form_type_range_value($element, $input = FALSE) {
  if ($input === '') {
    $offset = ($element['#max'] - $element['#min']) / 2;

    // Round to the step.
    if (strtolower($element['#step']) != 'any') {
      $steps = round($offset / $element['#step']);
      $offset = $element['#step'] * $steps;
    }

    return $element['#min'] + $offset;
  }
}

/**
 * Prepares a #type 'url' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_url($element) {
  $element['#attributes']['type'] = 'url';
  element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-url'));

  return $element;
}

/**
 * Prepares a #type 'search' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_search($element) {
  $element['#attributes']['type'] = 'search';
  element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-search'));

  return $element;
}

/**
 * Form element validation handler for #type 'url'.
 *
 * Note that #maxlength and #required is validated by _form_validate() already.
 */
function form_validate_url(&$element, &$form_state) {
  $value = trim($element['#value']);
  form_set_value($element, $value, $form_state);

  if ($value !== '' && !valid_url($value, TRUE)) {
    form_error($element, t('The URL %url is not valid.', array('%url' => $value)));
  }
}

/**
 * Form element validation handler for #type 'color'.
 */
function form_validate_color(&$element, &$form_state) {
  $value = trim($element['#value']);

  // Default to black if no value is given.
  // @see http://www.w3.org/TR/html5/number-state.html#color-state
  if ($value === '') {
    form_set_value($element, '#000000', $form_state);
  }
  else {
    // Try to parse the value and normalize it.
    try {
      form_set_value($element, Color::rgbToHex(Color::hexToRgb($value)), $form_state);
    }
    catch (InvalidArgumentException $e) {
      form_error($element, t('%name must be a valid color.', array('%name' => empty($element['#title']) ? $element['#parents'][0] : $element['#title'])));
    }
  }
}

/**
 * Prepares a #type 'color' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_color($element) {
  $element['#attributes']['type'] = 'color';
  element_set_attributes($element, array('id', 'name', 'value'));
  _form_set_attributes($element, array('form-color'));

  return $element;
}

/**
 * Returns HTML for a form.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #action, #method, #attributes, #children
 *
 * @ingroup themeable
 */
function theme_form($variables) {
  $element = $variables['element'];
  if (isset($element['#action'])) {
    $element['#attributes']['action'] = drupal_strip_dangerous_protocols($element['#action']);
  }
  element_set_attributes($element, array('method', 'id'));
  if (empty($element['#attributes']['accept-charset'])) {
    $element['#attributes']['accept-charset'] = "UTF-8";
  }
  // Anonymous DIV to satisfy XHTML compliance.
  return '<form' . new Attribute($element['#attributes']) . '><div>' . $element['#children'] . '</div></form>';
}

/**
 * Returns HTML for a textarea form element.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #value, #description, #rows, #cols,
 *     #placeholder, #required, #attributes, #resizable
 *
 * @ingroup themeable
 */
function theme_textarea($variables) {
  $element = $variables['element'];
  element_set_attributes($element, array('id', 'name', 'rows', 'cols', 'placeholder'));
  _form_set_attributes($element, array('form-textarea'));

  $wrapper_attributes = array(
    'class' => array('form-textarea-wrapper'),
  );

  // Add resizable behavior.
  if (!empty($element['#resizable'])) {
    $element['#attributes']['class'][] = 'resize-' . $element['#resizable'];
  }

  $output = '<div' . new Attribute($wrapper_attributes) . '>';
  $output .= '<textarea' . new Attribute($element['#attributes']) . '>' . check_plain($element['#value']) . '</textarea>';
  $output .= '</div>';
  return $output;
}

/**
 * Prepares a #type 'password' render element for theme_input().
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #value, #description, #size, #maxlength,
 *   #placeholder, #required, #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_password($element) {
  $element['#attributes']['type'] = 'password';
  element_set_attributes($element, array('id', 'name', 'size', 'maxlength', 'placeholder'));
  _form_set_attributes($element, array('form-text'));

  return $element;
}

/**
 * Expands a weight element into a select element.
 */
function form_process_weight($element) {
  $element['#is_weight'] = TRUE;

  // If the number of options is small enough, use a select field.
  $max_elements = config('system.site')->get('weight_select_max');
  if ($element['#delta'] <= $max_elements) {
    $element['#type'] = 'select';
    for ($n = (-1 * $element['#delta']); $n <= $element['#delta']; $n++) {
      $weights[$n] = $n;
    }
    $element['#options'] = $weights;
    $element += element_info('select');
  }
  // Otherwise, use a text field.
  else {
    $element['#type'] = 'number';
    // Use a field big enough to fit most weights.
    $element['#size'] = 10;
    $element += element_info('number');
  }

  return $element;
}

/**
 * Prepares a #type 'file' render element for theme_input().
 *
 * For assistance with handling the uploaded file correctly, see the API
 * provided by file.inc.
 *
 * @param array $element
 *   An associative array containing the properties of the element.
 *   Properties used: #title, #name, #size, #description, #required,
 *   #attributes.
 *
 * @return array
 *   The $element with prepared variables ready for theme_input().
 */
function form_pre_render_file($element) {
  $element['#attributes']['type'] = 'file';
  element_set_attributes($element, array('id', 'name', 'size'));
  _form_set_attributes($element, array('form-file'));

  return $element;
}

/**
 * Processes a file upload element, make use of #multiple if present.
 */
function form_process_file($element) {
  if ($element['#multiple']) {
    $element['#attributes'] = array('multiple' => 'multiple');
    $element['#name'] .= '[]';
  }
  return $element;
}

/**
 * Returns HTML for a form element.
 *
 * Each form element is wrapped in a DIV container having the following CSS
 * classes:
 * - form-item: Generic for all form elements.
 * - form-type-#type: The internal element #type.
 * - form-item-#name: The internal form element #name (usually derived from the
 *   $form structure and set via form_builder()).
 * - form-disabled: Only set if the form element is #disabled.
 *
 * In addition to the element itself, the DIV contains a label for the element
 * based on the optional #title_display property, and an optional #description.
 *
 * The optional #title_display property can have these values:
 * - before: The label is output before the element. This is the default.
 *   The label includes the #title and the required marker, if #required.
 * - after: The label is output after the element. For example, this is used
 *   for radio and checkbox #type elements as set in system_element_info().
 *   If the #title is empty but the field is #required, the label will
 *   contain only the required marker.
 * - invisible: Labels are critical for screen readers to enable them to
 *   properly navigate through forms but can be visually distracting. This
 *   property hides the label for everyone except screen readers.
 * - attribute: Set the title attribute on the element to create a tooltip
 *   but output no label element. This is supported only for checkboxes
 *   and radios in form_pre_render_conditional_form_element(). It is used
 *   where a visual label is not needed, such as a table of checkboxes where
 *   the row and column provide the context. The tooltip will include the
 *   title and required marker.
 *
 * If the #title property is not set, then the label and any required marker
 * will not be output, regardless of the #title_display or #required values.
 * This can be useful in cases such as the password_confirm element, which
 * creates children elements that have their own labels and required markers,
 * but the parent element should have neither. Use this carefully because a
 * field without an associated label can cause accessibility challenges.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #title_display, #description, #id, #required,
 *     #children, #type, #name.
 *
 * @ingroup themeable
 */
function theme_form_element($variables) {
  $element = &$variables['element'];

  // This function is invoked as theme wrapper, but the rendered form element
  // may not necessarily have been processed by form_builder().
  $element += array(
    '#title_display' => 'before',
  );

  // Take over any #wrapper_attributes defined by the element.
  // @todo Temporary hack for #type 'item'.
  // @see http://drupal.org/node/1829202
  if (isset($element['#wrapper_attributes'])) {
    $attributes = $element['#wrapper_attributes'];
  }
  // Add element #id for #type 'item'.
  if (isset($element['#markup']) && !empty($element['#id'])) {
    $attributes['id'] = $element['#id'];
  }
  // Add element's #type and #name as class to aid with JS/CSS selectors.
  $attributes['class'][] = 'form-item';
  if (!empty($element['#type'])) {
    $attributes['class'][] = 'form-type-' . strtr($element['#type'], '_', '-');
  }
  if (!empty($element['#name'])) {
    $attributes['class'][] = 'form-item-' . strtr($element['#name'], array(' ' => '-', '_' => '-', '[' => '-', ']' => ''));
  }
  // Add a class for disabled elements to facilitate cross-browser styling.
  if (!empty($element['#attributes']['disabled'])) {
    $attributes['class'][] = 'form-disabled';
  }
  $output = '<div' . new Attribute($attributes) . '>' . "\n";

  // If #title is not set, we don't display any label or required marker.
  if (!isset($element['#title'])) {
    $element['#title_display'] = 'none';
  }
  $prefix = isset($element['#field_prefix']) ? '<span class="field-prefix">' . $element['#field_prefix'] . '</span> ' : '';
  $suffix = isset($element['#field_suffix']) ? ' <span class="field-suffix">' . $element['#field_suffix'] . '</span>' : '';

  switch ($element['#title_display']) {
    case 'before':
    case 'invisible':
      $output .= ' ' . theme('form_element_label', $variables);
      $output .= ' ' . $prefix . $element['#children'] . $suffix . "\n";
      break;

    case 'after':
      $output .= ' ' . $prefix . $element['#children'] . $suffix;
      $output .= ' ' . theme('form_element_label', $variables) . "\n";
      break;

    case 'none':
    case 'attribute':
      // Output no label and no required marker, only the children.
      $output .= ' ' . $prefix . $element['#children'] . $suffix . "\n";
      break;
  }

  if (!empty($element['#description'])) {
    $attributes = array('class' => 'description');
    if (!empty($element['#id'])) {
      $attributes['id'] = $element['#id'] . '--description';
    }
    $output .= '<div' . new Attribute($attributes) . '>' . $element['#description'] . "</div>\n";
  }

  $output .= "</div>\n";

  return $output;
}

/**
 * Returns HTML for a marker for required form elements.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *
 * @ingroup themeable
 */
function theme_form_required_marker($variables) {
  // This is also used in the installer, pre-database setup.
  $t = get_t();
  $attributes = array(
    'class' => 'form-required',
    'title' => $t('This field is required.'),
  );
  return '<abbr' . new Attribute($attributes) . '>*</abbr>';
}

/**
 * Returns HTML for a form element label and required marker.
 *
 * Form element labels include the #title and a #required marker. The label is
 * associated with the element itself by the element #id. Labels may appear
 * before or after elements, depending on theme_form_element() and
 * #title_display.
 *
 * This function will not be called for elements with no labels, depending on
 * #title_display. For elements that have an empty #title and are not required,
 * this function will output no label (''). For required elements that have an
 * empty #title, this will output the required marker alone within the label.
 * The label will use the #id to associate the marker with the field that is
 * required. That is especially important for screenreader users to know
 * which field is required.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #required, #title, #id, #value, #description.
 *
 * @ingroup themeable
 */
function theme_form_element_label($variables) {
  $element = $variables['element'];
  // This is also used in the installer, pre-database setup.
  $t = get_t();

  // If title and required marker are both empty, output no label.
  if ((!isset($element['#title']) || $element['#title'] === '') && empty($element['#required'])) {
    return '';
  }

  // If the element is required, a required marker is appended to the label.
  $required = !empty($element['#required']) ? theme('form_required_marker', array('element' => $element)) : '';

  $title = filter_xss_admin($element['#title']);

  $attributes = array();
  // Style the label as class option to display inline with the element.
  if ($element['#title_display'] == 'after') {
    $attributes['class'] = 'option';
  }
  // Show label only to screen readers to avoid disruption in visual flows.
  elseif ($element['#title_display'] == 'invisible') {
    $attributes['class'] = 'element-invisible';
  }

  if (!empty($element['#id'])) {
    $attributes['for'] = $element['#id'];
  }

  return '<label' . new Attribute($attributes) . '>' . $t('!title!required', array('!title' => $title, '!required' => $required)) . '</label>';
}

/**
 * Sets a form element's class attribute.
 *
 * Adds 'required' and 'error' classes as needed.
 *
 * @param $element
 *   The form element.
 * @param $name
 *   Array of new class names to be added.
 */
function _form_set_attributes(&$element, $class = array()) {
  if (!empty($class)) {
    if (!isset($element['#attributes']['class'])) {
      $element['#attributes']['class'] = array();
    }
    $element['#attributes']['class'] = array_merge($element['#attributes']['class'], $class);
  }
  // This function is invoked from form element theme functions, but the
  // rendered form element may not necessarily have been processed by
  // form_builder().
  if (!empty($element['#required'])) {
    $element['#attributes']['class'][] = 'required';
    $element['#attributes']['required'] = 'required';
    $element['#attributes']['aria-required'] = 'true';
  }
  if (isset($element['#parents']) && form_get_error($element) !== NULL && !empty($element['#validated'])) {
    $element['#attributes']['class'][] = 'error';
  }
}

/**
 * @} End of "defgroup form_api".
 */

/**
 * @defgroup batch Batch operations
 * @{
 * Creates and processes batch operations.
 *
 * Functions allowing forms processing to be spread out over several page
 * requests, thus ensuring that the processing does not get interrupted
 * because of a PHP timeout, while allowing the user to receive feedback
 * on the progress of the ongoing operations.
 *
 * The API is primarily designed to integrate nicely with the Form API
 * workflow, but can also be used by non-Form API scripts (like update.php)
 * or even simple page callbacks (which should probably be used sparingly).
 *
 * Example:
 * @code
 * $batch = array(
 *   'title' => t('Exporting'),
 *   'operations' => array(
 *     array('my_function_1', array($account->uid, 'story')),
 *     array('my_function_2', array()),
 *   ),
 *   'finished' => 'my_finished_callback',
 *   'file' => 'path_to_file_containing_myfunctions',
 * );
 * batch_set($batch);
 * // Only needed if not inside a form _submit handler.
 * // Setting redirect in batch_process.
 * batch_process('node/1');
 * @endcode
 *
 * Note: if the batch 'title', 'init_message', 'progress_message', or
 * 'error_message' could contain any user input, it is the responsibility of
 * the code calling batch_set() to sanitize them first with a function like
 * check_plain() or filter_xss(). Furthermore, if the batch operation
 * returns any user input in the 'results' or 'message' keys of $context,
 * it must also sanitize them first.
 *
 * Sample batch operations:
 * @code
 * // Simple and artificial: load a node of a given type for a given user
 * function my_function_1($uid, $type, &$context) {
 *   // The $context array gathers batch context information about the execution (read),
 *   // as well as 'return values' for the current operation (write)
 *   // The following keys are provided :
 *   // 'results' (read / write): The array of results gathered so far by
 *   //   the batch processing, for the current operation to append its own.
 *   // 'message' (write): A text message displayed in the progress page.
 *   // The following keys allow for multi-step operations :
 *   // 'sandbox' (read / write): An array that can be freely used to
 *   //   store persistent data between iterations. It is recommended to
 *   //   use this instead of $_SESSION, which is unsafe if the user
 *   //   continues browsing in a separate window while the batch is processing.
 *   // 'finished' (write): A float number between 0 and 1 informing
 *   //   the processing engine of the completion level for the operation.
 *   //   1 (or no value explicitly set) means the operation is finished
 *   //   and the batch processing can continue to the next operation.
 *
 *   $nodes = entity_load_multiple_by_properties('node', array('uid' => $uid, 'type' => $type));
 *   $node = reset($nodes);
 *   $context['results'][] = $node->nid . ' : ' . check_plain($node->label());
 *   $context['message'] = check_plain($node->label());
 * }
 *
 * // More advanced example: multi-step operation - load all nodes, five by five
 * function my_function_2(&$context) {
 *   if (empty($context['sandbox'])) {
 *     $context['sandbox']['progress'] = 0;
 *     $context['sandbox']['current_node'] = 0;
 *     $context['sandbox']['max'] = db_query('SELECT COUNT(DISTINCT nid) FROM {node}')->fetchField();
 *   }
 *   $limit = 5;
 *   $result = db_select('node')
 *     ->fields('node', array('nid'))
 *     ->condition('nid', $context['sandbox']['current_node'], '>')
 *     ->orderBy('nid')
 *     ->range(0, $limit)
 *     ->execute();
 *   foreach ($result as $row) {
 *     $node = node_load($row->nid, TRUE);
 *     $context['results'][] = $node->nid . ' : ' . check_plain($node->label());
 *     $context['sandbox']['progress']++;
 *     $context['sandbox']['current_node'] = $node->nid;
 *     $context['message'] = check_plain($node->label());
 *   }
 *   if ($context['sandbox']['progress'] != $context['sandbox']['max']) {
 *     $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];
 *   }
 * }
 * @endcode
 *
 * Sample 'finished' callback:
 * @code
 * function batch_test_finished($success, $results, $operations) {
 *   // The 'success' parameter means no fatal PHP errors were detected. All
 *   // other error management should be handled using 'results'.
 *   if ($success) {
 *     $message = format_plural(count($results), 'One post processed.', '@count posts processed.');
 *   }
 *   else {
 *     $message = t('Finished with an error.');
 *   }
 *   drupal_set_message($message);
 *   // Providing data for the redirected page is done through $_SESSION.
 *   foreach ($results as $result) {
 *     $items[] = t('Loaded node %title.', array('%title' => $result));
 *   }
 *   $_SESSION['my_batch_results'] = $items;
 * }
 * @endcode
 */

/**
 * Adds a new batch.
 *
 * Batch operations are added as new batch sets. Batch sets are used to spread
 * processing (primarily, but not exclusively, forms processing) over several
 * page requests. This helps to ensure that the processing is not interrupted
 * due to PHP timeouts, while users are still able to receive feedback on the
 * progress of the ongoing operations. Combining related operations into
 * distinct batch sets provides clean code independence for each batch set,
 * ensuring that two or more batches, submitted independently, can be processed
 * without mutual interference. Each batch set may specify its own set of
 * operations and results, produce its own UI messages, and trigger its own
 * 'finished' callback. Batch sets are processed sequentially, with the progress
 * bar starting afresh for each new set.
 *
 * @param $batch_definition
 *   An associative array defining the batch, with the following elements (all
 *   are optional except as noted):
 *   - operations: (required) Array of function calls to be performed.
 *     Example:
 *     @code
 *     array(
 *       array('my_function_1', array($arg1)),
 *       array('my_function_2', array($arg2_1, $arg2_2)),
 *     )
 *     @endcode
 *   - title: A safe, translated string to use as the title for the progress
 *     page. Defaults to t('Processing').
 *   - init_message: Message displayed while the processing is initialized.
 *     Defaults to t('Initializing.').
 *   - progress_message: Message displayed while processing the batch. Available
 *     placeholders are @current, @remaining, @total, @percentage, @estimate and
 *     @elapsed. Defaults to t('Completed @current of @total.').
 *   - error_message: Message displayed if an error occurred while processing
 *     the batch. Defaults to t('An error has occurred.').
 *   - finished: Name of a function to be executed after the batch has
 *     completed. This should be used to perform any result massaging that may
 *     be needed, and possibly save data in $_SESSION for display after final
 *     page redirection.
 *   - file: Path to the file containing the definitions of the 'operations' and
 *     'finished' functions, for instance if they don't reside in the main
 *     .module file. The path should be relative to base_path(), and thus should
 *     be built using drupal_get_path().
 *   - css: Array of paths to CSS files to be used on the progress page.
 *   - url_options: options passed to url() when constructing redirect URLs for
 *     the batch.
 */
function batch_set($batch_definition) {
  if ($batch_definition) {
    $batch =& batch_get();

    // Initialize the batch if needed.
    if (empty($batch)) {
      $batch = array(
        'sets' => array(),
        'has_form_submits' => FALSE,
      );
    }

    // Base and default properties for the batch set.
    // Use get_t() to allow batches during installation.
    $t = get_t();
    $init = array(
      'sandbox' => array(),
      'results' => array(),
      'success' => FALSE,
      'start' => 0,
      'elapsed' => 0,
    );
    $defaults = array(
      'title' => $t('Processing'),
      'init_message' => $t('Initializing.'),
      'progress_message' => $t('Completed @current of @total.'),
      'error_message' => $t('An error has occurred.'),
      'css' => array(),
    );
    $batch_set = $init + $batch_definition + $defaults;

    // Tweak init_message to avoid the bottom of the page flickering down after
    // init phase.
    $batch_set['init_message'] .= '<br/>&nbsp;';

    // The non-concurrent workflow of batch execution allows us to save
    // numberOfItems() queries by handling our own counter.
    $batch_set['total'] = count($batch_set['operations']);
    $batch_set['count'] = $batch_set['total'];

    // Add the set to the batch.
    if (empty($batch['id'])) {
      // The batch is not running yet. Simply add the new set.
      $batch['sets'][] = $batch_set;
    }
    else {
      // The set is being added while the batch is running. Insert the new set
      // right after the current one to ensure execution order, and store its
      // operations in a queue.
      $index = $batch['current_set'] + 1;
      $slice1 = array_slice($batch['sets'], 0, $index);
      $slice2 = array_slice($batch['sets'], $index);
      $batch['sets'] = array_merge($slice1, array($batch_set), $slice2);
      _batch_populate_queue($batch, $index);
    }
  }
}

/**
 * Processes the batch.
 *
 * Unless the batch has been marked with 'progressive' = FALSE, the function
 * issues a drupal_goto and thus ends page execution.
 *
 * This function is generally not needed in form submit handlers;
 * Form API takes care of batches that were set during form submission.
 *
 * @param $redirect
 *   (optional) Path to redirect to when the batch has finished processing.
 * @param $url
 *   (optional - should only be used for separate scripts like update.php)
 *   URL of the batch processing page.
 * @param $redirect_callback
 *   (optional) Specify a function to be called to redirect to the progressive
 *   processing page. By default drupal_goto() will be used to redirect to a
 *   page which will do the progressive page. Specifying another function will
 *   allow the progressive processing to be processed differently.
 */
function batch_process($redirect = NULL, $url = 'batch', $redirect_callback = 'drupal_goto') {
  $batch =& batch_get();

  drupal_theme_initialize();

  if (isset($batch)) {
    // Add process information
    $process_info = array(
      'current_set' => 0,
      'progressive' => TRUE,
      'url' => $url,
      'url_options' => array(),
      'source_url' => current_path(),
      'redirect' => $redirect,
      'theme' => $GLOBALS['theme_key'],
      'redirect_callback' => $redirect_callback,
    );
    $batch += $process_info;

    // The batch is now completely built. Allow other modules to make changes
    // to the batch so that it is easier to reuse batch processes in other
    // environments.
    drupal_alter('batch', $batch);

    // Assign an arbitrary id: don't rely on a serial column in the 'batch'
    // table, since non-progressive batches skip database storage completely.
    $batch['id'] = db_next_id();

    // Move operations to a job queue. Non-progressive batches will use a
    // memory-based queue.
    foreach ($batch['sets'] as $key => $batch_set) {
      _batch_populate_queue($batch, $key);
    }

    // Initiate processing.
    if ($batch['progressive']) {
      // Now that we have a batch id, we can generate the redirection link in
      // the generic error message.
      $t = get_t();
      $batch['error_message'] = $t('Please continue to <a href="@error_url">the error page</a>', array('@error_url' => url($url, array('query' => array('id' => $batch['id'], 'op' => 'finished')))));

      // Clear the way for the drupal_goto() redirection to the batch processing
      // page, by saving and unsetting the 'destination', if there is any.
      if (isset($_GET['destination'])) {
        $batch['destination'] = $_GET['destination'];
        unset($_GET['destination']);
      }

      // Store the batch.
      db_insert('batch')
        ->fields(array(
          'bid' => $batch['id'],
          'timestamp' => REQUEST_TIME,
          'token' => drupal_get_token($batch['id']),
          'batch' => serialize($batch),
        ))
        ->execute();

      // Set the batch number in the session to guarantee that it will stay alive.
      $_SESSION['batches'][$batch['id']] = TRUE;

      // Redirect for processing.
      $function = $batch['redirect_callback'];
      $function($batch['url'], array('query' => array('op' => 'start', 'id' => $batch['id'])));
    }
    else {
      // Non-progressive execution: bypass the whole progressbar workflow
      // and execute the batch in one pass.
      require_once DRUPAL_ROOT . '/core/includes/batch.inc';
      _batch_process();
    }
  }
}

/**
 * Retrieves the current batch.
 */
function &batch_get() {
  // Not drupal_static(), because Batch API operates at a lower level than most
  // use-cases for resetting static variables, and we specifically do not want a
  // global drupal_static_reset() resetting the batch information. Functions
  // that are part of the Batch API and need to reset the batch information may
  // call batch_get() and manipulate the result by reference. Functions that are
  // not part of the Batch API can also do this, but shouldn't.
  static $batch = array();
  return $batch;
}

/**
 * Populates a job queue with the operations of a batch set.
 *
 * Depending on whether the batch is progressive or not, the
 * Drupal\Core\Queue\Batch or Drupal\Core\Queue\BatchMemory handler classes will
 * be used.
 *
 * @param $batch
 *   The batch array.
 * @param $set_id
 *   The id of the set to process.
 *
 * @return
 *   The name and class of the queue are added by reference to the batch set.
 */
function _batch_populate_queue(&$batch, $set_id) {
  $batch_set = &$batch['sets'][$set_id];

  if (isset($batch_set['operations'])) {
    $batch_set += array(
      'queue' => array(
        'name' => 'drupal_batch:' . $batch['id'] . ':' . $set_id,
        'class' => $batch['progressive'] ? 'Drupal\Core\Queue\Batch' : 'Drupal\Core\Queue\BatchMemory',
      ),
    );

    $queue = _batch_queue($batch_set);
    $queue->createQueue();
    foreach ($batch_set['operations'] as $operation) {
      $queue->createItem($operation);
    }

    unset($batch_set['operations']);
  }
}

/**
 * Returns a queue object for a batch set.
 *
 * @param $batch_set
 *   The batch set.
 *
 * @return
 *   The queue object.
 */
function _batch_queue($batch_set) {
  static $queues;

  if (!isset($queues)) {
    $queues = array();
  }

  if (isset($batch_set['queue'])) {
    $name = $batch_set['queue']['name'];
    $class = $batch_set['queue']['class'];

    if (!isset($queues[$class][$name])) {
      $queues[$class][$name] = new $class($name, Database::getConnection());
    }
    return $queues[$class][$name];
  }
}

/**
 * @} End of "defgroup batch".
 */