diff --git a/core/modules/filter/filter.admin-rtl.css b/core/modules/filter/filter.admin-rtl.css
index 10620bfac531a52b76e6e80710c4f41052b54b81..0370a980be5012861a180eadf66b3495c9911268 100644
--- a/core/modules/filter/filter.admin-rtl.css
+++ b/core/modules/filter/filter.admin-rtl.css
@@ -1,7 +1,7 @@
 
 /**
  * @file
- * RTL admin styling for the Filter module.
+ * Right-to-Left administrative styling for the Filter module.
  */
 
 /**
diff --git a/core/modules/filter/filter.admin.inc b/core/modules/filter/filter.admin.inc
index a62f8e3c14eb0ff90050aee4077e0407635a6893..e06719952dc169c43f0f54f03a39373891b489f8 100644
--- a/core/modules/filter/filter.admin.inc
+++ b/core/modules/filter/filter.admin.inc
@@ -2,11 +2,11 @@
 
 /**
  * @file
- * Admin page callbacks for the Filter module.
+ * Administrative page callbacks for the Filter module.
  */
 
 /**
- * Form constructor for a form to list and reorder text formats.
+ * Page callback: Form constructor for a form to list and reorder text formats.
  *
  * @see filter_menu()
  * @see filter_admin_overview_submit()
@@ -103,6 +103,7 @@ function filter_admin_overview_submit($form, &$form_state) {
  *     enabled (1) or not (0). Defaults to 1.
  *   - weight: (optional) The weight of the text format, which controls its
  *     placement in text format lists. If omitted, the weight is set to 0.
+ *     Defaults to NULL.
  *
  * @return
  *   A form array.
@@ -129,8 +130,8 @@ function filter_admin_format_page($format = NULL) {
  *     save. If this corresponds to an existing text format, that format will be
  *     updated; otherwise, a new format will be created.
  *   - name: The title of the text format.
- *   - cache: An integer indicating whether the text format is cacheable (1) or
- *     not (0). Defaults to 1.
+ *   - cache: (optional) An integer indicating whether the text format is
+ *     cacheable (1) or not (0). Defaults to 1.
  *   - status: (optional) An integer indicating whether the text format is
  *     enabled (1) or not (0). Defaults to 1.
  *   - weight: (optional) The weight of the text format, which controls its
@@ -283,7 +284,7 @@ function filter_admin_format_form($form, &$form_state, $format) {
 /**
  * Returns HTML for a text format's filter order form.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - element: A render element representing the form.
  *
@@ -365,7 +366,7 @@ function filter_admin_format_form_submit($form, &$form_state) {
 }
 
 /**
- * Form constructor for the text format deletion confirmation form.
+ * Page callback: Form constructor to confirm the text format deletion.
  *
  * @param $format
  *   An object representing a text format.
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index c4b596a4ab4b36373172460f5a1a7ad496f5929c..182bbb1cb469d2dc0a08a6e2ee07e119d526668b 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -359,6 +359,12 @@ function filter_format_exists($format_id) {
 /**
  * Displays a text format form title.
  *
+ * @param object $format_id
+ *   A format object.
+ *
+ * @return string
+ *   The name of the format.
+ *
  * @see filter_menu()
  */
 function filter_admin_format_title($format) {
@@ -434,7 +440,8 @@ function filter_modules_disabled($modules) {
  *
  * @param $account
  *   (optional) If provided, only those formats that are allowed for this user
- *   account will be returned. All formats will be returned otherwise.
+ *   account will be returned. All formats will be returned otherwise. Defaults
+ *   to NULL.
  *
  * @return
  *   An array of text format objects, keyed by the format ID and ordered by
@@ -547,7 +554,7 @@ function filter_get_formats_by_role($rid) {
  *
  * @param $account
  *   (optional) The user account to check. Defaults to the currently logged-in
- *   user.
+ *   user. Defaults to NULL.
  *
  * @return
  *   The ID of the user's default text format.
@@ -612,15 +619,15 @@ function filter_get_filter_types_by_format($format_id) {
  * format is initialized to output plain text. Installation profiles and site
  * administrators have the freedom to configure it further.
  *
- * Note that the fallback format is completely distinct from the default
- * format, which differs per user and is simply the first format which that
- * user has access to. The default and fallback formats are only guaranteed to
- * be the same for users who do not have access to any other format; otherwise,
- * the fallback format's weight determines its placement with respect to the
- * user's other formats.
+ * Note that the fallback format is completely distinct from the default format,
+ * which differs per user and is simply the first format which that user has
+ * access to. The default and fallback formats are only guaranteed to be the
+ * same for users who do not have access to any other format; otherwise, the
+ * fallback format's weight determines its placement with respect to the user's
+ * other formats.
  *
- * Any modules implementing a format deletion functionality must not delete
- * this format.
+ * Any modules implementing a format deletion functionality must not delete this
+ * format.
  *
  * @return
  *   The ID of the fallback text format.
@@ -640,6 +647,9 @@ function filter_fallback_format() {
 
 /**
  * Returns the title of the fallback text format.
+ *
+ * @return string
+ *   The title of the fallback text format.
  */
 function filter_fallback_format_title() {
   $fallback_format = filter_format_load(filter_fallback_format());
@@ -648,6 +658,9 @@ function filter_fallback_format_title() {
 
 /**
  * Returns a list of all filters provided by modules.
+ *
+ * @return array
+ *   An array of filter formats.
  */
 function filter_get_filters() {
   $filters = &drupal_static(__FUNCTION__, array());
@@ -799,16 +812,17 @@ function filter_list_format($format_id) {
  * @param $text
  *   The text to be filtered.
  * @param $format_id
- *   The format ID of the text to be filtered. If no format is assigned, the
- *   fallback format will be used.
+ *   (optional) The format ID of the text to be filtered. If no format is
+ *   assigned, the fallback format will be used. Defaults to NULL.
  * @param $langcode
- *   Optional: the language code of the text to be filtered, e.g. 'en' for
+ *   (optional) The language code of the text to be filtered, e.g. 'en' for
  *   English. This allows filters to be language aware so language specific
- *   text replacement can be implemented.
+ *   text replacement can be implemented. Defaults to an empty string.
  * @param $cache
- *   Boolean whether to cache the filtered output in the {cache_filter} table.
- *   The caller may set this to FALSE when the output is already cached
- *   elsewhere to avoid duplicate cache lookups and storage.
+ *   (optional) A Boolean indicating whether to cache the filtered output in the
+ *   {cache_filter} table. The caller may set this to FALSE when the output is
+ *   already cached elsewhere to avoid duplicate cache lookups and storage.
+ *   Defaults to FALSE.
  * @param array $filter_types_to_skip
  *   (optional) An array of filter types to skip, or an empty array (default)
  *   to skip no filter types. All of the format's filters will be applied,
@@ -1071,7 +1085,7 @@ function filter_form_access_denied($element) {
 /**
  * Returns HTML for a text format-enabled form element.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - element: A render element containing #children and #description.
  *
@@ -1096,7 +1110,7 @@ function theme_text_format_wrapper($variables) {
  *   An object representing the text format.
  * @param $account
  *   (optional) The user account to check access for; if omitted, the currently
- *   logged-in user is used.
+ *   logged-in user is used. Defaults to NULL.
  *
  * @return
  *   Boolean TRUE if the user is allowed to access the given format.
@@ -1232,9 +1246,11 @@ function filter_dom_serialize($dom_document) {
  * @param $dom_element
  *   The element potentially containing a CDATA node.
  * @param $comment_start
- *   String to use as a comment start marker to escape the CDATA declaration.
+ *   (optional) A string to use as a comment start marker to escape the CDATA
+ *   declaration. Defaults to '//'.
  * @param $comment_end
- *   String to use as a comment end marker to escape the CDATA declaration.
+ *   (optional) A string to use as a comment end marker to escape the CDATA
+ *   declaration. Defaults to an empty string.
  */
 function filter_dom_serialize_escape_cdata_element($dom_document, $dom_element, $comment_start = '//', $comment_end = '') {
   foreach ($dom_element->childNodes as $node) {
@@ -1269,7 +1285,7 @@ function theme_filter_tips_more_info() {
 /**
  * Returns HTML for guidelines for a text format.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - format: An object representing a text format.
  *
@@ -1695,8 +1711,9 @@ function _filter_url_parse_partial_links($match) {
  *   An array containing matches to replace from preg_replace_callback(),
  *   whereas $match[1] is expected to contain the content to be filtered.
  * @param $escape
- *   (optional) Boolean whether to escape (TRUE) or unescape comments (FALSE).
- *   Defaults to neither. If TRUE, statically cached $comments are reset.
+ *   (optional) A Boolean indicating whether to escape (TRUE) or unescape
+ *   comments (FALSE). Defaults to NULL, indicating neither. If TRUE, statically
+ *   cached $comments are reset.
  */
 function _filter_url_escape_comments($match, $escape = NULL) {
   static $mode, $comments = array();
diff --git a/core/modules/filter/filter.pages.inc b/core/modules/filter/filter.pages.inc
index dec59c3b3660c078079972442120470c10241ba3..5b20d4f0bb0ec7969189d69e858757b1b68af67f 100644
--- a/core/modules/filter/filter.pages.inc
+++ b/core/modules/filter/filter.pages.inc
@@ -8,7 +8,14 @@
 /**
  * Page callback: Displays a page with long filter tips.
  *
+ * @param $format
+ *   (optional) A filter format. Defaults to NULL.
+ *
+ * @return string
+ *   An HTML-formatted string.
+ *
  * @see filter_menu()
+ * @see theme_filter_tips()
  */
 function filter_tips_long($format = NULL) {
   if (!empty($format)) {
@@ -23,7 +30,7 @@ function filter_tips_long($format = NULL) {
 /**
  * Returns HTML for a set of filter tips.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - tips: An array containing descriptions and a CSS ID in the form of
  *     'module-name/filter-id' (only used when $long is TRUE) for each
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterAdminTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterAdminTest.php
index 9a09a76dc4a6a7c0d235b8d43d50a7c78c252040..c2b76d2b1c76f7ac650fcc9868c75b82b6fdd20b 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterAdminTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterAdminTest.php
@@ -9,7 +9,16 @@
 
 use Drupal\simpletest\WebTestBase;
 
+/**
+ * Tests the administrative functionality of the Filter module.
+ */
 class FilterAdminTest extends WebTestBase {
+
+  /**
+   * The installation profile to use with this test.
+   *
+   * @var string
+   */
   protected $profile = 'standard';
 
   public static function getInfo() {
@@ -36,6 +45,9 @@ function setUp() {
     $this->drupalLogin($this->admin_user);
   }
 
+  /**
+   * Tests the format administration functionality.
+   */
   function testFormatAdmin() {
     // Add text format.
     $this->drupalGet('admin/config/content/formats');
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
index 766736f4d550a80595b2defcfc2563857f881260..7b4c6f56ef71b07f443152419d4388de96c94512 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
@@ -82,7 +82,7 @@ function testTextFormatCrud() {
   }
 
   /**
-   * Verify that a text format is properly stored.
+   * Verifies that a text format is properly stored.
    */
   function verifyTextFormat($format) {
     $t_args = array('%format' => $format->name);
@@ -120,7 +120,7 @@ function verifyTextFormat($format) {
   }
 
   /**
-   * Verify that filters are properly stored for a text format.
+   * Verifies that filters are properly stored for a text format.
    */
   function verifyFilters($format) {
     // Verify filter database records.
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterDefaultFormatTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterDefaultFormatTest.php
index 04fa5205895098c878e68a4031e5f36ca64dc6af..103d7775a4ab4ebfe280e6802bafff247de13093 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterDefaultFormatTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterDefaultFormatTest.php
@@ -9,6 +9,9 @@
 
 use Drupal\simpletest\WebTestBase;
 
+/**
+ * Tests the default filter functionality in the Filter module.
+ */
 class FilterDefaultFormatTest extends WebTestBase {
   public static function getInfo() {
     return array(
@@ -64,7 +67,7 @@ function testDefaultTextFormats() {
   }
 
   /**
-   * Rebuild text format and permission caches in the thread running the tests.
+   * Rebuilds text format and permission caches in the thread running the tests.
    */
   protected function resetFilterCaches() {
     filter_formats_reset();
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterFormatAccessTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterFormatAccessTest.php
index 4636610c9e5a95bd9d694d774e0adf8f5d783156..a71a9e9f4ef70da54b558dea71b54f5dd3fc6405 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterFormatAccessTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterFormatAccessTest.php
@@ -9,11 +9,43 @@
 
 use Drupal\simpletest\WebTestBase;
 
+/**
+ * Tests the filter format access functionality in the Filter module.
+ */
 class FilterFormatAccessTest extends WebTestBase {
+  /**
+   * A user with administrative permissions.
+   *
+   * @var object
+   */
   protected $admin_user;
+
+  /**
+   * A user with 'administer filters' permission.
+   *
+   * @var object
+   */
   protected $filter_admin_user;
+
+  /**
+   * A user with permission to create and edit own content.
+   *
+   * @var object
+   */
   protected $web_user;
+
+  /**
+   * An object representing an allowed text format.
+   *
+   * @var object
+   */
   protected $allowed_format;
+
+  /**
+   * An object representing a disallowed text format.
+   *
+   * @var object
+   */
   protected $disallowed_format;
 
   public static function getInfo() {
@@ -69,6 +101,9 @@ function setUp() {
     ));
   }
 
+  /**
+   * Tests the Filter format access permissions functionality.
+   */
   function testFormatPermissions() {
     // Make sure that a regular user only has access to the text format they
     // were granted access to, as well to the fallback format.
@@ -154,11 +189,11 @@ function testFormatRoles() {
   /**
    * Tests editing a page using a disallowed text format.
    *
-   * Verifies that regular users and administrators are able to edit a page,
-   * but not allowed to change the fields which use an inaccessible text
-   * format. Also verifies that fields which use a text format that does not
-   * exist can be edited by administrators only, but that the administrator is
-   * forced to choose a new format before saving the page.
+   * Verifies that regular users and administrators are able to edit a page, but
+   * not allowed to change the fields which use an inaccessible text format.
+   * Also verifies that fields which use a text format that does not exist can
+   * be edited by administrators only, but that the administrator is forced to
+   * choose a new format before saving the page.
    */
   function testFormatWidgetPermissions() {
     $langcode = LANGUAGE_NOT_SPECIFIED;
@@ -274,7 +309,7 @@ function testFormatWidgetPermissions() {
   }
 
   /**
-   * Rebuild text format and permission caches in the thread running the tests.
+   * Rebuilds text format and permission caches in the thread running the tests.
    */
   protected function resetFilterCaches() {
     filter_formats_reset();
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterHooksTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterHooksTest.php
index f01b4d2eced55fdc98fd3650a68bd3bc6a135dd0..496a5f3a224a29bfd119b2446175c56054c36b37 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterHooksTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterHooksTest.php
@@ -10,7 +10,7 @@
 use Drupal\simpletest\WebTestBase;
 
 /**
- * Tests for filter hook invocation.
+ * Tests for Filter's hook invocations.
  */
 class FilterHooksTest extends WebTestBase {
 
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
index 813d717b0b79b8b561a612212c6412a7743dfd51..5928a4d29522bdde52dc36753f6750b450666166 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
@@ -21,6 +21,13 @@ class FilterSecurityTest extends WebTestBase {
    */
   public static $modules = array('node', 'php', 'filter_test');
 
+  /**
+   * A user with administrative permissions.
+   *
+   * @var object
+   */
+  protected $admin_user;
+
   public static function getInfo() {
     return array(
       'name' => 'Security',
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterSettingsTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterSettingsTest.php
index 0a6c00c70ce1d83a61d862853c47ef99b86b4964..6d2ab992ab4cfb5a468ed56a4711185cd453f132 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterSettingsTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterSettingsTest.php
@@ -13,6 +13,11 @@
  * Tests filter settings.
  */
 class FilterSettingsTest extends WebTestBase {
+  /**
+   * The installation profile to use with this test class.
+   *
+   * @var string
+   */
   protected $profile = 'testing';
 
   public static function getInfo() {
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterUnitTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterUnitTest.php
index b2264a4ed7ad0c8b34c03088c2b6e99b2b2e07c7..de9f194a9eae8186a7f9c88a6eb5ea2ae2856c91 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterUnitTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterUnitTest.php
@@ -981,9 +981,9 @@ function testHtmlCorrectorFilter() {
    * @param $needle
    *   Lowercase, plain text to look for.
    * @param $message
-   *   Message to display if failed.
+   *   (optional) Message to display if failed. Defaults to an empty string.
    * @param $group
-   *   The group this message belongs to, defaults to 'Other'.
+   *   (optional) The group this message belongs to. Defaults to 'Other'.
    * @return
    *   TRUE on pass, FALSE on fail.
    */
@@ -1005,9 +1005,9 @@ function assertNormalized($haystack, $needle, $message = '', $group = 'Other') {
    * @param $needle
    *   Lowercase, plain text to look for.
    * @param $message
-   *   Message to display if failed.
+   *   (optional) Message to display if failed. Defaults to an empty string.
    * @param $group
-   *   The group this message belongs to, defaults to 'Other'.
+   *   (optional) The group this message belongs to. Defaults to 'Other'.
    * @return
    *   TRUE on pass, FALSE on fail.
    */