'title' => The title to display.
    'description' => Description to display.
    'keyword' => Default keyword for the context created by this relationship.
    'required context' => One or more ctools_context_required/optional objects 
      describing the context input.
      new panels_required_context(t('Node'), 'node'),
    'context' => The callback to create the context. Params: ($context = NULL, $conf)
    'settings form' => Settings form. Params: $conf
    'settings form validate' => Validate.