system.api.php 175 KB
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<?php

/**
 * @file
 * Hooks provided by Drupal core and the System module.
 */

/**
 * @addtogroup hooks
 * @{
 */

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/**
 * Defines one or more hooks that are exposed by a module.
 *
 * Normally hooks do not need to be explicitly defined. However, by declaring a
 * hook explicitly, a module may define a "group" for it. Modules that implement
 * a hook may then place their implementation in either $module.module or in
 * $module.$group.inc. If the hook is located in $module.$group.inc, then that
 * file will be automatically loaded when needed.
 * In general, hooks that are rarely invoked and/or are very large should be
 * placed in a separate include file, while hooks that are very short or very
 * frequently called should be left in the main module file so that they are
 * always available.
 *
 * @return
 *   An associative array whose keys are hook names and whose values are an
 *   associative array containing:
 *   - group: A string defining the group to which the hook belongs. The module
 *     system will determine whether a file with the name $module.$group.inc
 *     exists, and automatically load it when required.
 *
 * See system_hook_info() for all hook groups defined by Drupal core.
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 *
 * @see hook_hook_info_alter().
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 */
function hook_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'tokens',
  );
  $hooks['tokens'] = array(
    'group' => 'tokens',
  );
  return $hooks;
}

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/**
 * Alter information from hook_hook_info().
 *
 * @param $hooks
 *   Information gathered by module_hook_info() from other modules'
 *   implementations of hook_hook_info(). Alter this array directly.
 *   See hook_hook_info() for information on what this may contain.
 */
function hook_hook_info_alter(&$hooks) {
  // Our module wants to completely override the core tokens, so make
  // sure the core token hooks are not found.
  $hooks['token_info']['group'] = 'mytokens';
  $hooks['tokens']['group'] = 'mytokens';
}

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/**
 * Inform the base system and the Field API about one or more entity types.
 *
 * Inform the system about one or more entity types (i.e., object types that
 * can be loaded via entity_load() and, optionally, to which fields can be
 * attached).
 *
 * @return
 *   An array whose keys are entity type names and whose values identify
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 *   properties of those types that the system needs to know about:
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 *   - label: The human-readable name of the type.
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 *   - controller class: The name of the class that is used to load the objects.
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 *     The class has to implement the DrupalEntityControllerInterface interface.
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 *     Leave blank to use the DrupalDefaultEntityController implementation.
 *   - base table: (used by DrupalDefaultEntityController) The name of the
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 *     entity type's base table.
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 *   - revision table: The name of the entity type's revision table (if any).
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 *   - static cache: (used by DrupalDefaultEntityController) FALSE to disable
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 *     static caching of entities during a page request. Defaults to TRUE.
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 *   - field cache: (used by Field API loading and saving of field data) FALSE
 *     to disable Field API's persistent cache of field data. Only recommended
 *     if a higher level persistent cache is available for the entity type.
 *     Defaults to TRUE.
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 *   - load hook: The name of the hook which should be invoked by
 *     DrupalDefaultEntityController:attachLoad(), for example 'node_load'.
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 *   - uri callback: A function taking an entity as argument and returning the
 *     uri elements of the entity, e.g. 'path' and 'options'. The actual entity
 *     uri can be constructed by passing these elements to url().
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 *   - label callback: (optional) A function taking an entity type and an entity
 *     as arguments and returning the label of the entity. The entity label is
 *     the main string associated with an entity; for example, the title of a
 *     node or the subject of a comment. If there is an entity object property
 *     that defines the label, use the 'label' element of the 'entity keys'
 *     return value component to provide this information (see below). If more
 *     complex logic is needed to determine the label of an entity, you can
 *     instead specify a callback function here, which will be called to
 *     determine the entity label. See also the entity_label() function, which
 *     implements this logic.
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 *   - fieldable: Set to TRUE if you want your entity type to accept fields
 *     being attached to it.
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 *   - translation: An associative array of modules registered as field
 *     translation handlers. Array keys are the module names, array values
 *     can be any data structure the module uses to provide field translation.
 *     Any empty value disallows the module to appear as a translation handler.
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 *   - entity keys: An array describing how the Field API can extract the
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 *     information it needs from the objects of the type. Elements:
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 *     - id: The name of the property that contains the primary id of the
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 *       entity. Every entity object passed to the Field API must have this
 *       property and its value must be numeric.
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 *     - revision: The name of the property that contains the revision id of
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 *       the entity. The Field API assumes that all revision ids are unique
 *       across all entities of a type. This entry can be omitted if the
 *       entities of this type are not versionable.
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 *     - bundle: The name of the property that contains the bundle name for the
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 *       entity. The bundle name defines which set of fields are attached to
 *       the entity (e.g. what nodes call "content type"). This entry can be
 *       omitted if this entity type exposes a single bundle (all entities have
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 *       the same collection of fields). The name of this single bundle will be
 *       the same as the entity type.
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 *     - label: The name of the property that contains the entity label. For
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 *       example, if the entity's label is located in $entity->subject, then
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 *       'subject' should be specified here. If complex logic is required to
 *       build the label, a 'label callback' should be defined instead (see
 *       the 'label callback' section above for details).
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 *   - bundle keys: An array describing how the Field API can extract the
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 *     information it needs from the bundle objects for this type. This entry
 *     is required if the 'path' provided in the 'bundles'/'admin' section
 *     identifies the bundle using a named menu placeholder whose loader
 *     callback returns an object (e.g., $vocabulary for taxonomy terms, or
 *     $node_type for nodes). If the path does not include the bundle, or the
 *     bundle is just a string rather than an automatically loaded object, then
 *     this can be omitted. Elements:
 *     - bundle: The name of the property of the bundle object that contains
 *       the name of the bundle object.
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 *   - bundles: An array describing all bundles for this object type. Keys are
 *     bundles machine names, as found in the objects' 'bundle' property
 *     (defined in the 'entity keys' entry above). Elements:
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 *     - label: The human-readable name of the bundle.
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 *     - uri callback: Same as the 'uri callback' key documented above for the
 *       entity type, but for the bundle only. When determining the URI of an
 *       entity, if a 'uri callback' is defined for both the entity type and
 *       the bundle, the one for the bundle is used.
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 *     - admin: An array of information that allows Field UI pages to attach
 *       themselves to the existing administration pages for the bundle.
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 *       Elements:
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 *       - path: the path of the bundle's main administration page, as defined
 *         in hook_menu(). If the path includes a placeholder for the bundle,
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 *         the 'bundle argument' and 'real path' keys below are required.
 *       - bundle argument: The position of the bundle placeholder in 'path', if
 *         any.
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 *       - real path: The actual path (no placeholder) of the bundle's main
 *         administration page. This will be used to generate links.
 *       - access callback: As in hook_menu(). 'user_access' will be assumed if
 *         no value is provided.
 *       - access arguments: As in hook_menu().
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 *   - view modes: An array describing the view modes for the entity type. View
 *     modes let entities be displayed differently depending on the context.
 *     For instance, a node can be displayed differently on its own page
 *     ('full' mode), on the home page or taxonomy listings ('teaser' mode), or
 *     in an RSS feed ('rss' mode). Modules taking part in the display of the
 *     entity (notably the Field API) can adjust their behavior depending on
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 *     the requested view mode. An additional 'default' view mode is available
 *     for all entity types. This view mode is not intended for actual entity
 *     display, but holds default display settings. For each available view
 *     mode, administrators can configure whether it should use its own set of
 *     field display settings, or just replicate the settings of the 'default'
 *     view mode, thus reducing the amount of display configurations to keep
 *     track of. Keys of the array are view mode names. Each view mode is
 *     described by an array with the following key/value pairs:
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 *     - label: The human-readable name of the view mode
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 *     - custom settings: A boolean specifying whether the view mode should by
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 *       default use its own custom field display settings. If FALSE, entities
 *       displayed in this view mode will reuse the 'default' display settings
 *       by default (e.g. right after the module exposing the view mode is
 *       enabled), but administrators can later use the Field UI to apply custom
 *       display settings specific to the view mode.
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 *
 * @see entity_load()
 * @see hook_entity_info_alter()
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 */
function hook_entity_info() {
  $return = array(
    'node' => array(
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      'label' => t('Node'),
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      'controller class' => 'NodeController',
      'base table' => 'node',
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      'revision table' => 'node_revision',
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      'uri callback' => 'node_uri',
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      'fieldable' => TRUE,
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      'translation' => array(
        'locale' => TRUE,
      ),
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      'entity keys' => array(
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        'id' => 'nid',
        'revision' => 'vid',
        'bundle' => 'type',
      ),
      'bundle keys' => array(
        'bundle' => 'type',
      ),
      'bundles' => array(),
      'view modes' => array(
        'full' => array(
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          'label' => t('Full content'),
          'custom settings' => FALSE,
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        ),
        'teaser' => array(
          'label' => t('Teaser'),
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          'custom settings' => TRUE,
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        ),
        'rss' => array(
          'label' => t('RSS'),
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          'custom settings' => FALSE,
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        ),
      ),
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    ),
  );
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  // Search integration is provided by node.module, so search-related
  // view modes for nodes are defined here and not in search.module.
  if (module_exists('search')) {
    $return['node']['view modes'] += array(
      'search_index' => array(
        'label' => t('Search index'),
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        'custom settings' => FALSE,
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      ),
      'search_result' => array(
        'label' => t('Search result'),
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        'custom settings' => FALSE,
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      ),
    );
  }

  // Bundles must provide a human readable name so we can create help and error
  // messages, and the path to attach Field admin pages to.
  foreach (node_type_get_names() as $type => $name) {
    $return['node']['bundles'][$type] = array(
      'label' => $name,
      'admin' => array(
        'path' => 'admin/structure/types/manage/%node_type',
        'real path' => 'admin/structure/types/manage/' . str_replace('_', '-', $type),
        'bundle argument' => 4,
        'access arguments' => array('administer content types'),
      ),
    );
  }

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  return $return;
}

/**
 * Alter the entity info.
 *
 * Modules may implement this hook to alter the information that defines an
 * entity. All properties that are available in hook_entity_info() can be
 * altered here.
 *
 * @param $entity_info
 *   The entity info array, keyed by entity name.
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 *
 * @see hook_entity_info()
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 */
function hook_entity_info_alter(&$entity_info) {
  // Set the controller class for nodes to an alternate implementation of the
  // DrupalEntityController interface.
  $entity_info['node']['controller class'] = 'MyCustomNodeController';
}

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/**
 * Act on entities when loaded.
 *
 * This is a generic load hook called for all entity types loaded via the
 * entity API.
 *
 * @param $entities
 *   The entities keyed by entity ID.
 * @param $type
 *   The type of entities being loaded (i.e. node, user, comment).
 */
function hook_entity_load($entities, $type) {
  foreach ($entities as $entity) {
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    $entity->foo = mymodule_add_something($entity, $type);
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  }
}

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/**
 * Act on an entity before it is about to be created or updated.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being saved (i.e. node, user, comment).
 */
function hook_entity_presave($entity, $type) {
  $entity->changed = REQUEST_TIME;
}

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/**
 * Act on entities when inserted.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being inserted (i.e. node, user, comment).
 */
function hook_entity_insert($entity, $type) {
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  // Insert the new entity into a fictional table of all entities.
  $info = entity_get_info($type);
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  list($id) = entity_extract_ids($type, $entity);
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  db_insert('example_entity')
    ->fields(array(
      'type' => $type,
      'id' => $id,
      'created' => REQUEST_TIME,
      'updated' => REQUEST_TIME,
    ))
    ->execute();
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}

/**
 * Act on entities when updated.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being updated (i.e. node, user, comment).
 */
function hook_entity_update($entity, $type) {
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  // Update the entity's entry in a fictional table of all entities.
  $info = entity_get_info($type);
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  list($id) = entity_extract_ids($type, $entity);
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  db_update('example_entity')
    ->fields(array(
      'updated' => REQUEST_TIME,
    ))
    ->condition('type', $type)
    ->condition('id', $id)
    ->execute();
}

/**
 * Act on entities when deleted.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being deleted (i.e. node, user, comment).
 */
function hook_entity_delete($entity, $type) {
  // Delete the entity's entry from a fictional table of all entities.
  $info = entity_get_info($type);
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  list($id) = entity_extract_ids($type, $entity);
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  db_delete('example_entity')
    ->condition('type', $type)
    ->condition('id', $id)
    ->execute();
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}

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/**
 * Alter or execute an EntityFieldQuery.
 *
 * @param EntityFieldQuery $query
 *   An EntityFieldQuery. One of the most important properties to be changed is
 *   EntityFieldQuery::executeCallback. If this is set to an existing function,
 *   this function will get the query as its single argument and its result
 *   will be the returned as the result of EntityFieldQuery::execute(). This can
 *   be used to change the behavior of EntityFieldQuery entirely. For example,
 *   the default implementation can only deal with one field storage engine, but
 *   it is possible to write a module that can query across field storage
 *   engines. Also, the default implementation presumes entities are stored in
 *   SQL, but the execute callback could instead query any other entity storage,
 *   local or remote.
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 *
 *   Note the $query->altered attribute which is TRUE in case the query has
 *   already been altered once. This happens with cloned queries.
 *   If there is a pager, then such a cloned query will be executed to count
 *   all elements. This query can be detected by checking for
 *   ($query->pager && $query->count), allowing the driver to return 0 from
 *   the count query and disable the pager.
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 */
function hook_entity_query_alter($query) {
  $query->executeCallback = 'my_module_query_callback';
}

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/**
 * Act on entities being assembled before rendering.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being rendered (i.e. node, user, comment).
 * @param $view_mode
 *   The view mode the entity is rendered in.
 * @param $langcode
 *   The language code used for rendering.
 *
 * The module may add elements to $entity->content prior to rendering. The
 * structure of $entity->content is a renderable array as expected by
 * drupal_render().
 *
 * @see hook_entity_view_alter()
 * @see hook_comment_view()
 * @see hook_node_view()
 * @see hook_user_view()
 */
function hook_entity_view($entity, $type, $view_mode, $langcode) {
  $entity->content['my_additional_field'] = array(
    '#markup' => $additional_field,
    '#weight' => 10,
    '#theme' => 'mymodule_my_additional_field',
  );
}

/**
 * Alter the results of ENTITY_view().
 *
 * This hook is called after the content has been assembled in a structured
 * array and may be used for doing processing which requires that the complete
 * entity content structure has been built.
 *
 * If a module wishes to act on the rendered HTML of the entity rather than the
 * structured content array, it may use this hook to add a #post_render
 * callback. Alternatively, it could also implement hook_preprocess_ENTITY().
 * See drupal_render() and theme() for details.
 *
 * @param $build
 *   A renderable array representing the entity content.
 * @param $type
 *   The type of entity being rendered (i.e. node, user, comment).
 *
 * @see hook_entity_view()
 * @see hook_comment_view_alter()
 * @see hook_node_view_alter()
 * @see hook_taxonomy_term_view_alter()
 * @see hook_user_view_alter()
 */
function hook_entity_view_alter(&$build, $type) {
  if ($build['#view_mode'] == 'full' && isset($build['an_additional_field'])) {
    // Change its weight.
    $build['an_additional_field']['#weight'] = -10;

    // Add a #post_render callback to act on the rendered HTML of the entity.
    $build['#post_render'][] = 'my_module_node_post_render';
  }
}

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/**
 * Define administrative paths.
 *
 * Modules may specify whether or not the paths they define in hook_menu() are
 * to be considered administrative. Other modules may use this information to
 * display those pages differently (e.g. in a modal overlay, or in a different
 * theme).
 *
 * To change the administrative status of menu items defined in another module's
 * hook_menu(), modules should implement hook_admin_paths_alter().
 *
 * @return
 *   An associative array. For each item, the key is the path in question, in
 *   a format acceptable to drupal_match_path(). The value for each item should
 *   be TRUE (for paths considered administrative) or FALSE (for non-
 *   administrative paths).
 *
 * @see hook_menu()
 * @see drupal_match_path()
 * @see hook_admin_paths_alter()
 */
function hook_admin_paths() {
  $paths = array(
    'mymodule/*/add' => TRUE,
    'mymodule/*/edit' => TRUE,
  );
  return $paths;
}

/**
 * Redefine administrative paths defined by other modules.
 *
 * @param $paths
 *   An associative array of administrative paths, as defined by implementations
 *   of hook_admin_paths().
 *
 * @see hook_admin_paths()
 */
function hook_admin_paths_alter(&$paths) {
  // Treat all user pages as administrative.
  $paths['user'] = TRUE;
  $paths['user/*'] = TRUE;
  // Treat the forum topic node form as a non-administrative page.
  $paths['node/add/forum'] = FALSE;
}

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/**
 * Act on entities as they are being prepared for view.
 *
 * Allows you to operate on multiple entities as they are being prepared for
 * view. Only use this if attaching the data during the entity_load() phase
 * is not appropriate, for example when attaching other 'entity' style objects.
 *
 * @param $entities
 *   The entities keyed by entity ID.
 * @param $type
 *   The type of entities being loaded (i.e. node, user, comment).
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 * @param $langcode
 *   The language to display the entity in.
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 */
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function hook_entity_prepare_view($entities, $type, $langcode) {
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  // Load a specific node into the user object for later theming.
  if ($type == 'user') {
    $nodes = mymodule_get_user_nodes(array_keys($entities));
    foreach ($entities as $uid => $entity) {
      $entity->user_node = $nodes[$uid];
    }
  }
}

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/**
 * Perform periodic actions.
 *
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 * Modules that require some commands to be executed periodically can
 * implement hook_cron(). The engine will then call the hook whenever a cron
 * run happens, as defined by the administrator. Typical tasks managed by
 * hook_cron() are database maintenance, backups, recalculation of settings
 * or parameters, automated mailing, and retrieving remote data.
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 *
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 * Short-running or non-resource-intensive tasks can be executed directly in
 * the hook_cron() implementation.
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 *
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 * Long-running tasks and tasks that could time out, such as retrieving remote
 * data, sending email, and intensive file tasks, should use the queue API
 * instead of executing the tasks directly. To do this, first define one or
 * more queues via hook_cron_queue_info(). Then, add items that need to be
 * processed to the defined queues.
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 */
function hook_cron() {
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  // Short-running operation example, not using a queue:
  // Delete all expired records since the last cron run.
  $expires = variable_get('mymodule_cron_last_run', REQUEST_TIME);
  db_delete('mymodule_table')
    ->condition('expires', $expires, '>=')
    ->execute();
  variable_set('mymodule_cron_last_run', REQUEST_TIME);
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  // Long-running operation example, leveraging a queue:
  // Fetch feeds from other sites.
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  $result = db_query('SELECT * FROM {aggregator_feed} WHERE checked + refresh < :time AND refresh <> :never', array(
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    ':time' => REQUEST_TIME,
    ':never' => AGGREGATOR_CLEAR_NEVER,
  ));
  $queue = DrupalQueue::get('aggregator_feeds');
  foreach ($result as $feed) {
    $queue->createItem($feed);
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  }
}

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/**
 * Declare queues holding items that need to be run periodically.
 *
 * While there can be only one hook_cron() process running at the same time,
 * there can be any number of processes defined here running. Because of
 * this, long running tasks are much better suited for this API. Items queued
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 * in hook_cron() might be processed in the same cron run if there are not many
 * items in the queue, otherwise it might take several requests, which can be
 * run in parallel.
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 *
 * @return
 *   An associative array where the key is the queue name and the value is
 *   again an associative array. Possible keys are:
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 *   - 'worker callback': The name of the function to call. It will be called
 *     with one argument, the item created via DrupalQueue::createItem() in
 *     hook_cron().
 *   - 'time': (optional) How much time Drupal should spend on calling this
 *     worker in seconds. Defaults to 15.
 *
 * @see hook_cron()
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 * @see hook_cron_queue_info_alter()
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 */
function hook_cron_queue_info() {
  $queues['aggregator_feeds'] = array(
    'worker callback' => 'aggregator_refresh',
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    'time' => 60,
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  );
  return $queues;
}

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/**
 * Alter cron queue information before cron runs.
 *
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 * Called by drupal_cron_run() to allow modules to alter cron queue settings
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 * before any jobs are processesed.
 *
 * @param array $queues
 *   An array of cron queue information.
 *
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 * @see hook_cron_queue_info()
 * @see drupal_cron_run()
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 */
function hook_cron_queue_info_alter(&$queues) {
  // This site has many feeds so let's spend 90 seconds on each cron run
  // updating feeds instead of the default 60.
  $queues['aggregator_feeds']['time'] = 90;
}

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/**
 * Allows modules to declare their own Forms API element types and specify their
 * default values.
 *
 * This hook allows modules to declare their own form element types and to
 * specify their default values. The values returned by this hook will be
 * merged with the elements returned by hook_form() implementations and so
 * can return defaults for any Form APIs keys in addition to those explicitly
 * mentioned below.
 *
 * Each of the form element types defined by this hook is assumed to have
 * a matching theme function, e.g. theme_elementtype(), which should be
 * registered with hook_theme() as normal.
 *
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 * For more information about custom element types see the explanation at
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 * http://drupal.org/node/169815.
 *
 * @return
 *  An associative array describing the element types being defined. The array
 *  contains a sub-array for each element type, with the machine-readable type
 *  name as the key. Each sub-array has a number of possible attributes:
 *  - "#input": boolean indicating whether or not this element carries a value
 *    (even if it's hidden).
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 *  - "#process": array of callback functions taking $element, $form_state,
 *    and $complete_form.
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 *  - "#after_build": array of callback functions taking $element and $form_state.
 *  - "#validate": array of callback functions taking $form and $form_state.
 *  - "#element_validate": array of callback functions taking $element and
 *    $form_state.
 *  - "#pre_render": array of callback functions taking $element and $form_state.
 *  - "#post_render": array of callback functions taking $element and $form_state.
 *  - "#submit": array of callback functions taking $form and $form_state.
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 *  - "#title_display": optional string indicating if and how #title should be
 *    displayed, see theme_form_element() and theme_form_element_label().
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 *
 * @see hook_element_info_alter()
 * @see system_element_info()
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 */
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function hook_element_info() {
  $types['filter_format'] = array(
    '#input' => TRUE,
  );
  return $types;
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}

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/**
 * Alter the element type information returned from modules.
 *
 * A module may implement this hook in order to alter the element type defaults
 * defined by a module.
 *
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 * @param $type
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 *   All element type defaults as collected by hook_element_info().
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 *
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 * @see hook_element_info()
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 */
function hook_element_info_alter(&$type) {
  // Decrease the default size of textfields.
  if (isset($type['textfield']['#size'])) {
    $type['textfield']['#size'] = 40;
  }
}

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/**
 * Perform cleanup tasks.
 *
 * This hook is run at the end of each page request. It is often used for
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 * page logging and specialized cleanup. This hook MUST NOT print anything.
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 *
 * Only use this hook if your code must run even for cached page views.
 * If you have code which must run once on all non cached pages, use
 * hook_init instead. Thats the usual case. If you implement this hook
 * and see an error like 'Call to undefined function', it is likely that
 * you are depending on the presence of a module which has not been loaded yet.
 * It is not loaded because Drupal is still in bootstrap mode.
 *
 * @param $destination
 *   If this hook is invoked as part of a drupal_goto() call, then this argument
 *   will be a fully-qualified URL that is the destination of the redirect.
 */
function hook_exit($destination = NULL) {
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  db_update('counter')
    ->expression('hits', 'hits + 1')
    ->condition('type', 1)
    ->execute();
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}

/**
 * Perform necessary alterations to the JavaScript before it is presented on
 * the page.
 *
 * @param $javascript
 *   An array of all JavaScript being presented on the page.
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 *
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 * @see drupal_add_js()
 * @see drupal_get_js()
 * @see drupal_js_defaults()
 */
function hook_js_alter(&$javascript) {
  // Swap out jQuery to use an updated version of the library.
  $javascript['misc/jquery.js']['data'] = drupal_get_path('module', 'jquery_update') . '/jquery.js';
}

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/**
 * Registers JavaScript/CSS libraries associated with a module.
 *
 * Modules implementing this return an array of arrays. The key to each
 * sub-array is the machine readable name of the library. Each library may
 * contain the following items:
 *
 * - 'title': The human readable name of the library.
 * - 'website': The URL of the library's web site.
 * - 'version': A string specifying the version of the library; intentionally
 *   not a float because a version like "1.2.3" is not a valid float. Use PHP's
 *   version_compare() to compare different versions.
 * - 'js': An array of JavaScript elements; each element's key is used as $data
 *   argument, each element's value is used as $options array for
 *   drupal_add_js(). To add library-specific (not module-specific) JavaScript
 *   settings, the key may be skipped, the value must specify
 *   'type' => 'setting', and the actual settings must be contained in a 'data'
 *   element of the value.
 * - 'css': Like 'js', an array of CSS elements passed to drupal_add_css().
 * - 'dependencies': An array of libraries that are required for a library. Each
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 *   element is an array listing the module and name of another library. Note
 *   that all dependencies for each dependent library will also be added when
 *   this library is added.
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 *
 * Registered information for a library should contain re-usable data only.
 * Module- or implementation-specific data and integration logic should be added
 * separately.
 *
 * @return
 *   An array defining libraries associated with a module.
 *
 * @see system_library()
 * @see drupal_add_library()
 * @see drupal_get_library()
 */
function hook_library() {
  // Library One.
  $libraries['library-1'] = array(
    'title' => 'Library One',
    'website' => 'http://example.com/library-1',
    'version' => '1.2',
    'js' => array(
      drupal_get_path('module', 'my_module') . '/library-1.js' => array(),
    ),
    'css' => array(
      drupal_get_path('module', 'my_module') . '/library-2.css' => array(
        'type' => 'file',
        'media' => 'screen',
      ),
    ),
  );
  // Library Two.
  $libraries['library-2'] = array(
    'title' => 'Library Two',
    'website' => 'http://example.com/library-2',
    'version' => '3.1-beta1',
    'js' => array(
      // JavaScript settings may use the 'data' key.
      array(
        'type' => 'setting',
        'data' => array('library2' => TRUE),
      ),
    ),
    'dependencies' => array(
      // Require jQuery UI core by System module.
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      array('system', 'ui'),
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      // Require our other library.
      array('my_module', 'library-1'),
      // Require another library.
      array('other_module', 'library-3'),
    ),
  );
  return $libraries;
}

/**
 * Alters the JavaScript/CSS library registry.
 *
 * Allows certain, contributed modules to update libraries to newer versions
 * while ensuring backwards compatibility. In general, such manipulations should
 * only be done by designated modules, since most modules that integrate with a
 * certain library also depend on the API of a certain library version.
 *
 * @param $libraries
 *   The JavaScript/CSS libraries provided by $module. Keyed by internal library
 *   name and passed by reference.
 * @param $module
 *   The name of the module that registered the libraries.
 *
 * @see hook_library()
 */
function hook_library_alter(&$libraries, $module) {
  // Update Farbtastic to version 2.0.
  if ($module == 'system' && isset($libraries['farbtastic'])) {
    // Verify existing version is older than the one we are updating to.
    if (version_compare($libraries['farbtastic']['version'], '2.0', '<')) {
      // Update the existing Farbtastic to version 2.0.
      $libraries['farbtastic']['version'] = '2.0';
      $libraries['farbtastic']['js'] = array(
        drupal_get_path('module', 'farbtastic_update') . '/farbtastic-2.0.js' => array(),
      );
    }
  }
}

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/**
 * Alter CSS files before they are output on the page.
 *
 * @param $css
 *   An array of all CSS items (files and inline CSS) being requested on the page.
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 *
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 * @see drupal_add_css()
 * @see drupal_get_css()
 */
function hook_css_alter(&$css) {
  // Remove defaults.css file.
  unset($css[drupal_get_path('module', 'system') . '/defaults.css']);
}

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/**
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 * Alter the commands that are sent to the user through the Ajax framework.
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 *
 * @param $commands
 *   An array of all commands that will be sent to the user.
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 *
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 * @see ajax_render()
 */
function hook_ajax_render_alter($commands) {
  // Inject any new status messages into the content area.
  $commands[] = ajax_command_prepend('#block-system-main .content', theme('status_messages'));
}

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/**
 * Add elements to a page before it is rendered.
 *
 * Use this hook when you want to add elements at the page level. For your
 * additions to be printed, they have to be placed below a top level array key
 * of the $page array that has the name of a region of the active theme.
 *
 * By default, valid region keys are 'page_top', 'header', 'sidebar_first',
 * 'content', 'sidebar_second' and 'page_bottom'. To get a list of all regions
 * of the active theme, use system_region_list($theme). Note that $theme is a
 * global variable.
 *
 * If you want to alter the elements added by other modules or if your module
 * depends on the elements of other modules, use hook_page_alter() instead which
 * runs after this hook.
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
 * @see hook_page_alter()
 * @see drupal_render_page()
 */
function hook_page_build(&$page) {
  if (menu_get_object('node', 1)) {
    // We are on a node detail page. Append a standard disclaimer to the
    // content region.
    $page['content']['disclaimer'] = array(
      '#markup' => t('Acme, Inc. is not responsible for the contents of this sample code.'),
      '#weight' => 25,
    );
  }
}

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/**
 * Alter a menu router item right after it has been retrieved from the database or cache.
 *
 * This hook is invoked by menu_get_item() and allows for run-time alteration of router
 * information (page_callback, title, and so on) before it is translated and checked for
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 * access. The passed-in $router_item is statically cached for the current request, so this
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 * hook is only invoked once for any router item that is retrieved via menu_get_item().
 *
 * Usually, modules will only want to inspect the router item and conditionally
 * perform other actions (such as preparing a state for the current request).
 * Note that this hook is invoked for any router item that is retrieved by
 * menu_get_item(), which may or may not be called on the path itself, so implementations
 * should check the $path parameter if the alteration should fire for the current request
 * only.
 *
 * @param $router_item
 *   The menu router item for $path.
 * @param $path
 *   The originally passed path, for which $router_item is responsible.
 * @param $original_map
 *   The path argument map, as contained in $path.
 *
 * @see menu_get_item()
 */
function hook_menu_get_item_alter(&$router_item, $path, $original_map) {
  // When retrieving the router item for the current path...
  if ($path == $_GET['q']) {
    // ...call a function that prepares something for this request.
    mymodule_prepare_something();
  }
}

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/**
 * Define menu items and page callbacks.
 *
 * This hook enables modules to register paths in order to define how URL
 * requests are handled. Paths may be registered for URL handling only, or they
 * can register a link to be placed in a menu (usually the Navigation menu). A
 * path and its associated information is commonly called a "menu router item".
 * This hook is rarely called (for example, when modules are enabled), and
 * its results are cached in the database.
 *
 * hook_menu() implementations return an associative array whose keys define
 * paths and whose values are an associative array of properties for each
 * path. (The complete list of properties is in the return value section below.)
 *
 * The definition for each path may include a page callback function, which is
 * invoked when the registered path is requested. If there is no other
 * registered path that fits the requested path better, any further path
 * components are passed to the callback function. For example, your module
 * could register path 'abc/def':
 * @code
 *   function mymodule_menu() {
 *     $items['abc/def'] = array(
 *       'page callback' => 'mymodule_abc_view',
 *     );
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 *     return $items;
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 *   }
 *
 *   function mymodule_abc_view($ghi = 0, $jkl = '') {
 *     // ...
 *   }
 * @endcode
 * When path 'abc/def' is requested, no further path components are in the
 * request, and no additional arguments are passed to the callback function (so
 * $ghi and $jkl would take the default values as defined in the function
 * signature). When 'abc/def/123/foo' is requested, $ghi will be '123' and
 * $jkl will be 'foo'. Note that this automatic passing of optional path
 * arguments applies only to page and theme callback functions.
 *
 * In addition to optional path arguments, the page callback and other callback
 * functions may specify argument lists as arrays. These argument lists may
 * contain both fixed/hard-coded argument values and integers that correspond
 * to path components. When integers are used and the callback function is
 * called, the corresponding path components will be substituted for the
 * integers. That is, the integer 0 in an argument list will be replaced with
 * the first path component, integer 1 with the second, and so on (path
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 * components are numbered starting from zero). To pass an integer without it
 * being replaced with its respective path component, use the string value of
 * the integer (e.g., '1') as the argument value. This substitution feature
 * allows you to re-use a callback function for several different paths. For
 * example:
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 * @code
 *   function mymodule_menu() {
 *     $items['abc/def'] = array(
 *       'page callback' => 'mymodule_abc_view',
 *       'page arguments' => array(1, 'foo'),
 *     );
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 *     return $items;
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 *   }
 * @endcode
 * When path 'abc/def' is requested, the page callback function will get 'def'
 * as the first argument and (always) 'foo' as the second argument.
 *
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 * If a page callback function uses an argument list array, and its path is
 * requested with optional path arguments, then the list array's arguments are
 * passed to the callback function first, followed by the optional path
 * arguments. Using the above example, when path 'abc/def/bar/baz' is requested,
 * mymodule_abc_view() will be called with 'def', 'foo', 'bar' and 'baz' as
 * arguments, in that order.
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 *
 * Special care should be taken for the page callback drupal_get_form(), because
 * your specific form callback function will always receive $form and
 * &$form_state as the first function arguments:
 * @code
 *   function mymodule_abc_form($form, &$form_state) {
 *     // ...
 *     return $form;
 *   }
 * @endcode
 * See @link form_api Form API documentation @endlink for details.
 *
 * Wildcards within paths also work with integer substitution. For example,
 * your module could register path 'my-module/%/edit':
 * @code
 *   $items['my-module/%/edit'] = array(
 *     'page callback' => 'mymodule_abc_edit',
 *     'page arguments' => array(1),
 *   );
 * @endcode
 * When path 'my-module/foo/edit' is requested, integer 1 will be replaced
 * with 'foo' and passed to the callback function.
 *
 * Registered paths may also contain special "auto-loader" wildcard components
 * in the form of '%mymodule_abc', where the '%' part means that this path
 * component is a wildcard, and the 'mymodule_abc' part defines the prefix for a
 * load function, which here would be named mymodule_abc_load(). When a matching
 * path is requested, your load function will receive as its first argument the
 * path component in the position of the wildcard; load functions may also be
 * passed additional arguments (see "load arguments" in the return value
 * section below). For example, your module could register path
 * 'my-module/%mymodule_abc/edit':
 * @code
 *   $items['my-module/%mymodule_abc/edit'] = array(
 *     'page callback' => 'mymodule_abc_edit',
 *     'page arguments' => array(1),
 *   );
 * @endcode
 * When path 'my-module/123/edit' is requested, your load function
 * mymodule_abc_load() will be invoked with the argument '123', and should
 * load and return an "abc" object with internal id 123:
 * @code
 *   function mymodule_abc_load($abc_id) {
 *     return db_query("SELECT * FROM {mymodule_abc} WHERE abc_id = :abc_id", array(':abc_id' => $abc_id))->fetchObject();
 *   }
 * @endcode
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 * This 'abc' object will then be passed into the callback functions defined
 * for the menu item, such as the page callback function mymodule_abc_edit()
 * to replace the integer 1 in the argument array.
 *
 * You can also define a %wildcard_to_arg() function (for the example menu
 * entry above this would be 'mymodule_abc_to_arg()'). The _to_arg() function
 * is invoked to retrieve a value that is used in the path in place of the
 * wildcard. A good example is user.module, which defines
 * user_uid_optional_to_arg() (corresponding to the menu entry
 * 'user/%user_uid_optional'). This function returns the user ID of the
 * current user.
 *
 * The _to_arg() function will get called with three arguments:
 * - $arg: A string representing whatever argument may have been supplied by
 *   the caller (this is particularly useful if you want the _to_arg()
 *   function only supply a (default) value if no other value is specified,
 *   as in the case of user_uid_optional_to_arg().
 * - $map: An array of all path fragments (e.g. array('node','123','edit') for
 *   'node/123/edit').
 * - $index: An integer indicating which element of $map corresponds to $arg.
 *
 * _load() and _to_arg() functions may seem similar at first glance, but they
 * have different purposes and are called at different times. _load()
 * functions are called when the menu system is collecting arguments to pass
 * to the callback functions defined for the menu item. _to_arg() functions
 * are called when the menu system is generating links to related paths, such
 * as the tabs for a set of MENU_LOCAL_TASK items.
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 *
 * You can also make groups of menu items to be rendered (by default) as tabs
 * on a page. To do that, first create one menu item of type MENU_NORMAL_ITEM,
 * with your chosen path, such as 'foo'. Then duplicate that menu item, using a
 * subdirectory path, such as 'foo/tab1', and changing the type to
 * MENU_DEFAULT_LOCAL_TASK to make it the default tab for the group. Then add
 * the additional tab items, with paths such as "foo/tab2" etc., with type
 * MENU_LOCAL_TASK. Example:
 * @code
 * // Make "Foo settings" appear on the admin Config page
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 * $items['admin/config/system/foo'] = array(
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 *   'title' => 'Foo settings',
 *   'type' => MENU_NORMAL_ITEM,
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 *   // Page callback, etc. need to be added here.
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 * );
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 * // Make "Tab 1" the main tab on the "Foo settings" page
 * $items['admin/config/system/foo/tab1'] = array(
 *   'title' => 'Tab 1',
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 *   'type' => MENU_DEFAULT_LOCAL_TASK,
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 *   // Access callback, page callback, and theme callback will be inherited
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 *   // from 'admin/config/system/foo', if not specified here to override.
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 * );
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 * // Make an additional tab called "Tab 2" on "Foo settings"
 * $items['admin/config/system/foo/tab2'] = array(
 *   'title' => 'Tab 2',
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 *   'type' => MENU_LOCAL_TASK,
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 *   // Page callback and theme callback will be inherited from
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 *   // 'admin/config/system/foo', if not specified here to override.
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 *   // Need to add access callback or access arguments.
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 * );
 * @endcode
 *
 * @return
 *   An array of menu items. Each menu item has a key corresponding to the
 *   Drupal path being registered. The corresponding array value is an
 *   associative array that may contain the following key-value pairs:
 *   - "title": Required. The untranslated title of the menu item.
 *   - "title callback": Function to generate the title; defaults to t().
 *     If you require only the raw string to be output, set this to FALSE.
 *   - "title arguments": Arguments to send to t() or your custom callback,
 *     with path component substitution as described above.
 *   - "description": The untranslated description of the menu item.
 *   - "page callback": The function to call to display a web page when the user
 *     visits the path. If omitted, the parent menu item's callback will be used
 *     instead.
 *   - "page arguments": An array of arguments to pass to the page callback
 *     function, with path component substitution as described above.
 *   - "delivery callback": The function to call to package the result of the
 *     page callback function and send it to the browser. Defaults to
 *     drupal_deliver_html_page() unless a value is inherited from a parent menu
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 *     item. Note that this function is called even if the access checks fail,
 *     so any custom delivery callback function should take that into account.
 *     See drupal_deliver_html_page() for an example.
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 *   - "access callback": A function returning TRUE if the user has access
 *     rights to this menu item, and FALSE if not. It can also be a boolean
 *     constant instead of a function, and you can also use numeric values
 *     (will be cast to boolean). Defaults to user_access() unless a value is
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 *     inherited from the parent menu item; only MENU_DEFAULT_LOCAL_TASK items
 *     can inherit access callbacks. To use the user_access() default callback,
 *     you must specify the permission to check as 'access arguments' (see
 *     below).
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 *   - "access arguments": An array of arguments to pass to the access callback
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 *     function, with path component substitution as described above. If the
 *     access callback is inherited (see above), the access arguments will be
 *     inherited with it, unless overridden in the child menu item.
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 *   - "theme callback": (optional) A function returning the machine-readable
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 *     name of the theme that will be used to render the page. If not provided,
 *     the value will be inherited from a parent menu item. If there is no
 *     theme callback, or if the function does not return the name of a current
 *     active theme on the site, the theme for this page will be determined by
 *     either hook_custom_theme() or the default theme instead. As a general
 *     rule, the use of theme callback functions should be limited to pages
 *     whose functionality is very closely tied to a particular theme, since
 *     they can only be overridden by modules which specifically target those
 *     pages in hook_menu_alter(). Modules implementing more generic theme
 *     switching functionality (for example, a module which allows the theme to
 *     be set dynamically based on the current user's role) should use
 *     hook_custom_theme() instead.
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 *   - "theme arguments": An array of arguments to pass to the theme callback
 *     function, with path component substitution as described above.
 *   - "file": A file that will be included before the page callback is called;
 *     this allows page callback functions to be in separate files. The file
 *     should be relative to the implementing module's directory unless
 *     otherwise specified by the "file path" option. Does not apply to other
 *     callbacks (only page callback).
 *   - "file path": The path to the directory containing the file specified in
 *     "file". This defaults to the path to the module implementing the hook.
 *   - "load arguments": An array of arguments to be passed to each of the
 *     wildcard object loaders in the path, after the path argument itself.
 *     For example, if a module registers path node/%node/revisions/%/view
 *     with load arguments set to array(3), the '%node' in the path indicates
 *     that the loader function node_load() will be called with the second
 *     path component as the first argument. The 3 in the load arguments
 *     indicates that the fourth path component will also be passed to
 *     node_load() (numbering of path components starts at zero). So, if path
 *     node/12/revisions/29/view is requested, node_load(12, 29) will be called.
 *     There are also two "magic" values that can be used in load arguments.
 *     "%index" indicates the index of the wildcard path component. "%map"
 *     indicates the path components as an array. For example, if a module
 *     registers for several paths of the form 'user/%user_category/edit/*', all
 *     of them can use the same load function user_category_load(), by setting
 *     the load arguments to array('%map', '%index'). For instance, if the user
 *     is editing category 'foo' by requesting path 'user/32/edit/foo', the load
 *     function user_category_load() will be called with 32 as its first
 *     argument, the array ('user', 32, 'edit', 'foo') as the map argument,
 *     and 1 as the index argument (because %user_category is the second path
 *     component and numbering starts at zero). user_category_load() can then
 *     use these values to extract the information that 'foo' is the category
 *     being requested.
 *   - "weight": An integer that determines the relative position of items in
 *     the menu; higher-weighted items sink. Defaults to 0. Menu items with the
 *     same weight are ordered alphabetically.
 *   - "menu_name": Optional. Set this to a custom menu if you don't want your
 *     item to be placed in Navigation.
 *   - "context": (optional) Defines the context a tab may appear in. By
 *     default, all tabs are only displayed as local tasks when being rendered
 *     in a page context. All tabs that should be accessible as contextual links
 *     in page region containers outside of the parent menu item's primary page
 *     context should be registered using one of the following contexts:
 *     - MENU_CONTEXT_PAGE: (default) The tab is displayed as local task for the
 *       page context only.
 *     - MENU_CONTEXT_INLINE: The tab is displayed as contextual link outside of
 *       the primary page context only.
 *     Contexts can be combined. For example, to display a tab both on a page
 *     and inline, a menu router item may specify:
 *     @code
 *       'context' => MENU_CONTEXT_PAGE | MENU_CONTEXT_INLINE,
 *     @endcode
 *   - "tab_parent": For local task menu items, the path of the task's parent
 *     item; defaults to the same path without the last component (e.g., the
 *     default parent for 'admin/people/create' is 'admin/people').
 *   - "tab_root": For local task menu items, the path of the closest non-tab
 *     item; same default as "tab_parent".
 *   - "position": Position of the block ('left' or 'right') on the system
 *     administration page for this item.
 *   - "type": A bitmask of flags describing properties of the menu item.
 *     Many shortcut bitmasks are provided as constants in menu.inc:
 *     - MENU_NORMAL_ITEM: Normal menu items show up in the menu tree and can be
 *       moved/hidden by the administrator.
 *     - MENU_CALLBACK: Callbacks simply register a path so that the correct
 *       information is generated when the path is accessed.
 *     - MENU_SUGGESTED_ITEM: Modules may "suggest" menu items that the
 *       administrator may enable.
 *     - MENU_LOCAL_ACTION: Local actions are menu items that describe actions
 *       on the parent item such as adding a new user or block, and are
 *       rendered in the action-links list in your theme.
 *     - MENU_LOCAL_TASK: Local tasks are menu items that describe different
 *       displays of data, and are generally rendered as tabs.
 *     - MENU_DEFAULT_LOCAL_TASK: Every set of local tasks should provide one
 *       "default" task, which should display the same page as the parent item.
 *     If the "type" element is omitted, MENU_NORMAL_ITEM is assumed.
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 *   - "options": An array of options to be passed to l() when generating a link
 *     from this menu item.
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 *
 * For a detailed usage example, see page_example.module.
 * For comprehensive documentation on the menu system, see
 * http://drupal.org/node/102338.
 */
function hook_menu() {
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  $items['example'] = array(
    'title' => 'Example Page',
    'page callback' => 'example_page',
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    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
  );
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  $items['example/feed'] = array(
    'title' => 'Example RSS feed',
    'page callback' => 'example_feed',
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    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Alter the data being saved to the {menu_router} table after hook_menu is invoked.
 *
 * This hook is invoked by menu_router_build(). The menu definitions are passed
 * in by reference. Each element of the $items array is one item returned
 * by a module from hook_menu. Additional items may be added, or existing items
 * altered.
 *
 * @param $items
 *   Associative array of menu router definitions returned from hook_menu().
 */
function hook_menu_alter(&$items) {
  // Example - disable the page at node/add
  $items['node/add']['access callback'] = FALSE;
}

/**
 * Alter the data being saved to the {menu_links} table by menu_link_save().
 *
 * @param $item
 *   Associative array defining a menu link as passed into menu_link_save().
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 *
 * @see hook_translated_menu_link_alter()
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 */
function hook_menu_link_alter(&$item) {
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  // Make all new admin links hidden (a.k.a disabled).
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  if (strpos($item['link_path'], 'admin') === 0 && empty($item['mlid'])) {
    $item['hidden'] = 1;
  }
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  // Flag a link to be altered by hook_translated_menu_link_alter().
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  if ($item['link_path'] == 'devel/cache/clear') {
    $item['options']['alter'] = TRUE;
  }
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  // Flag a link to be altered by hook_translated_menu_link_alter(), but only
  // if it is derived from a menu router item; i.e., do not alter a custom
  // menu link pointing to the same path that has been created by a user.
  if ($item['link_path'] == 'user' && $item['module'] == 'system') {
    $item['options']['alter'] = TRUE;
  }
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}

/**
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 * Alter a menu link after it has been translated and before it is rendered.
 *
 * This hook is invoked from _menu_link_translate() after a menu link has been
 * translated; i.e., after dynamic path argument placeholders (%) have been
 * replaced with actual values, the user access to the link's target page has
 * been checked, and the link has been localized. It is only invoked if
 * $item['options']['alter'] has been set to a non-empty value (e.g., TRUE).
 * This flag should be set using hook_menu_link_alter().
 *
 * Implementations of this hook are able to alter any property of the menu link.
 * For example, this hook may be used to add a page-specific query string to all
 * menu links, or hide a certain link by setting:
 * @code
 *   'hidden' => 1,
 * @endcode
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 *
 * @param $item
 *   Associative array defining a menu link after _menu_link_translate()
 * @param $map
 *   Associative array containing the menu $map (path parts and/or objects).
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 *
 * @see hook_menu_link_alter()
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 */
function hook_translated_menu_link_alter(&$item, $map) {
  if ($item['href'] == 'devel/cache/clear') {
    $item['localized_options']['query'] = drupal_get_destination();
  }
}

/**
 * Inform modules that a menu link has been created.
 *
 * This hook is used to notify modules that menu items have been
 * created. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_update()
 * @see hook_menu_link_delete()
 */
function hook_menu_link_insert($link) {
  // In our sample case, we track menu items as editing sections
  // of the site. These are stored in our table as 'disabled' items.
  $record['mlid'] = $link['mlid'];
  $record['menu_name'] = $link['menu_name'];
  $record['status'] = 0;
  drupal_write_record('menu_example', $record);
}

/**
 * Inform modules that a menu link has been updated.
 *
 * This hook is used to notify modules that menu items have been
 * updated. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_insert()
 * @see hook_menu_link_delete()
 */
function hook_menu_link_update($link) {
  // If the parent menu has changed, update our record.
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  $menu_name = db_query("SELECT menu_name FROM {menu_example} WHERE mlid = :mlid", array(':mlid' => $link['mlid']))->fetchField();
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  if ($menu_name != $link['menu_name']) {
    db_update('menu_example')
      ->fields(array('menu_name' => $link['menu_name']))
      ->condition('mlid', $link['mlid'])
      ->execute();
  }
}

/**
 * Inform modules that a menu link has been deleted.
 *
 * This hook is used to notify modules that menu items have been
 * deleted. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_insert()
 * @see hook_menu_link_update()
 */
function hook_menu_link_delete($link) {
  // Delete the record from our table.
  db_delete('menu_example')
    ->condition('mlid', $link['mlid'])
    ->execute();
}

/**
 * Alter tabs and actions displayed on the page before they are rendered.
 *
 * This hook is invoked by menu_local_tasks(). The system-determined tabs and
 * actions are passed in by reference. Additional tabs or actions may be added,
 * or existing items altered.
 *
 * Each tab or action is an associative array containing:
 * - #theme: The theme function to use to render.
 * - #link: An associative array containing:
 *   - title: The localized title of the link.
 *   - href: The system path to link to.
 *   - localized_options: An array of options to pass to url().
 * - #active: Whether the link should be marked as 'active'.
 *
 * @param $data
 *   An associative array containing:
 *   - actions: An associative array containing:
 *     - count: The amount of actions determined by the menu system, which can
 *       be ignored.
 *     - output: A list of of actions, each one being an associative array
 *       as described above.
 *   - tabs: An indexed array (list) of tab levels (up to 2 levels), each
 *     containing an associative array:
 *     - count: The amount of tabs determined by the menu system. This value
 *       does not need to be altered if there is more than one tab.
 *     - output: A list of of tabs, each one being an associative array as
 *       described above.
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 * @param $router_item
 *   The menu system router item of the page.
 * @param $root_path
 *   The path to the root item for this set of tabs.
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 */
function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
  // Add an action linking to node/add to all pages.
  $data['actions']['output'][] = array(
    '#theme' => 'menu_local_task',
    '#link' => array(
      'title' => t('Add new content'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add new content'),
        ),
      ),
    ),
  );

  // Add a tab linking to node/add to all pages.
  $data['tabs'][0]['output'][] = array(
    '#theme' => 'menu_local_task',
    '#link' => array(
      'title' => t('Example tab'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add new content'),
        ),
      ),
    ),
    // Define whether this link is active. This can be omitted for
    // implementations that add links to pages outside of the current page
    // context.
    '#active' => ($router_item['path'] == $root_path),
  );
}

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/**
 * Alter links in the active trail before it is rendered as the breadcrumb.
 *
 * This hook is invoked by menu_get_active_breadcrumb() and allows alteration
 * of the breadcrumb links for the current page, which may be preferred instead
 * of setting a custom breadcrumb via drupal_set_breadcrumb().
 *
 * Implementations should take into account that menu_get_active_breadcrumb()
 * subsequently performs the following adjustments to the active trail *after*
 * this hook has been invoked:
 * - The last link in $active_trail is removed, if its 'href' is identical to
 *   the 'href' of $item. This happens, because the breadcrumb normally does
 *   not contain a link to the current page.
 * - The (second to) last link in $active_trail is removed, if the current $item
 *   is a MENU_DEFAULT_LOCAL_TASK. This happens in order to do not show a link
 *   to the current page, when being on the path for the default local task;
 *   e.g. when being on the path node/%/view, the breadcrumb should not contain
 *   a link to node/%.
 *
 * Each link in the active trail must contain:
 * - title: The localized title of the link.
 * - href: The system path to link to.
 * - localized_options: An array of options to pass to url().
 *
 * @param $active_trail
 *   An array containing breadcrumb links for the current page.
 * @param $item
 *   The menu router item of the current page.
 *
 * @see drupal_set_breadcrumb()
 * @see menu_get_active_breadcrumb()
 * @see menu_get_active_trail()
 * @see menu_set_active_trail()
 */
function hook_menu_breadcrumb_alter(&$active_trail, $item) {
  // Always display a link to the current page by duplicating the last link in
  // the active trail. This means that menu_get_active_breadcrumb() will remove
  // the last link (for the current page), but since it is added once more here,
  // it will appear.
  if (!drupal_is_front_page()) {
    $end = end($active_trail);
    if ($item['href'] == $end['href']) {
      $active_trail[] = $end;
    }
  }
}

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/**
 * Alter contextual links before they are rendered.
 *
 * This hook is invoked by menu_contextual_links(). The system-determined
 * contextual links are passed in by reference. Additional links may be added
 * or existing links can be altered.
 *
 * Each contextual link must at least contain:
 * - title: The localized title of the link.
 * - href: The system path to link to.
 * - localized_options: An array of options to pass to url().
 *
 * @param $links
 *   An associative array containing contextual links for the given $root_path,
 *   as described above. The array keys are used to build CSS class names for
 *   contextual links and must therefore be unique for each set of contextual
 *   links.
 * @param $router_item
 *   The menu router item belonging to the $root_path being requested.
 * @param $root_path
 *   The (parent) path that has been requested to build contextual links for.
 *   This is a normalized path, which means that an originally passed path of
 *   'node/123' became 'node/%'.
 *
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 * @see hook_contextual_links_view_alter()
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 * @see menu_contextual_links()
 * @see hook_menu()
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 * @see contextual_preprocess()
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 */
function hook_menu_contextual_links_alter(&$links, $router_item, $root_path) {
  // Add a link to all contextual links for nodes.
  if ($root_path == 'node/%') {
    $links['foo'] = array(
      'title' => t('Do fu'),
      'href' => 'foo/do',
      'localized_options' => array(
        'query' => array(
          'foo' => 'bar',
        ),
      ),
    );
  }
}

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/**
 * Perform alterations before a page is rendered.
 *
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 * Use this hook when you want to remove or alter elements at the page
 * level, or add elements at the page level that depend on an other module's
 * elements (this hook runs after hook_page_build().
 *
 * If you are making changes to entities such as forms, menus, or user
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 * profiles, use those objects' native alter hooks instead (hook_form_alter(),
 * for example).
 *
 * The $page array contains top level elements for each block region:
 * @code
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 *   $page['page_top']
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 *   $page['header']
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 *   $page['sidebar_first']
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 *   $page['content']
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 *   $page['sidebar_second']
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 *   $page['page_bottom']
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 * @endcode
 *
 * The 'content' element contains the main content of the current page, and its
 * structure will vary depending on what module is responsible for building the
 * page. Some legacy modules may not return structured content at all: their
 * pre-rendered markup will be located in $page['content']['main']['#markup'].
 *
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 * Pages built by Drupal's core Node module use a standard structure:
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 *
 * @code
 *   // Node body.
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 *   $page['content']['system_main']['nodes'][$nid]['body']
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 *   // Array of links attached to the node (add comments, read more).
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 *   $page['content']['system_main']['nodes'][$nid]['links']
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 *   // The node object itself.
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 *   $page['content']['system_main']['nodes'][$nid]['#node']
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 *   // The results pager.
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 *   $page['content']['system_main']['pager']
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 * @endcode
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 *
 * Blocks may be referenced by their module/delta pair within a region:
 * @code
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 *   // The login block in the first sidebar region.
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 *   $page['sidebar_first']['user_login']['#block'];
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 * @endcode
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
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 * @see hook_page_build()
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 * @see drupal_render_page()
 */
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function hook_page_alter(&$page) {
  // Add help text to the user login block.
  $page['sidebar_first']['user_login']['help'] = array(
    '#weight' => -10,
    '#markup' => t('To post comments or add new content, you first have to log in.'),
  );
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}

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/**
 * Perform alterations before a form is rendered.
 *
 * One popular use of this hook is to add form elements to the node form. When
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 * altering a node form, the node object can be accessed at $form['#node'].
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 *
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 * Note that instead of hook_form_alter(), which is called for all forms, you
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 * can also use hook_form_FORM_ID_alter() to alter a specific form. For each
 * module (in system weight order) the general form alter hook implementation
 * is invoked first, then the form ID specific alter implementation is called.
 * After all module hook implementations are invoked, the hook_form_alter()
 * implementations from themes are invoked in the same manner.
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 *
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 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
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 *   A keyed array containing the current state of the form. The arguments
 *   that drupal_get_form() was originally called with are available in the
 *   array $form_state['build_info']['args'].
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 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
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 *
 * @see hook_form_FORM_ID_alter()
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 */
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function hook_form_alter(&$form, &$form_state, $form_id) {
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  if (isset($form['type']) && $form['type']['#value'] . '_node_settings' == $form_id) {
    $form['workflow']['upload_' . $form['type']['#value']] = array(
      '#type' => 'radios',
      '#title' => t('Attachments'),
      '#default_value' => variable_get('upload_' . $form['type']['#value'], 1),
      '#options' => array(t('Disabled'), t('Enabled')),
    );
  }
}

/**
 * Provide a form-specific alteration instead of the global hook_form_alter().
 *
 * Modules can implement hook_form_FORM_ID_alter() to modify a specific form,
 * rather than implementing hook_form_alter() and checking the form ID, or
 * using long switch statements to alter multiple forms.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
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 *   A keyed array containing the current state of the form. The arguments
 *   that drupal_get_form() was originally called with are available in the
 *   array $form_state['build_info']['args'].
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 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
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 *
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 * @see hook_form_alter()
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 * @see drupal_prepare_form()
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 */
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function hook_form_FORM_ID_alter(&$form, &$form_state, $form_id) {
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  // Modification for the form with the given form ID goes here. For example, if
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  // FORM_ID is "user_register_form" this code would run only on the user
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  // registration form.

  // Add a checkbox to registration form about agreeing to terms of use.
  $form['terms_of_use'] = array(
    '#type' => 'checkbox',
    '#title' => t("I agree with the website's terms and conditions."),
    '#required' => TRUE,
  );
}

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/**
 * Provide a form-specific alteration for shared forms.
 *
 * Modules can implement hook_form_BASE_FORM_ID_alter() to modify a specific
 * form belonging to multiple form_ids, rather than implementing
 * hook_form_alter() and checking for conditions that would identify the
 * shared form constructor.
 *
 * Examples for such forms are node_form() or comment_form().
 *
 * Note that this hook fires after hook_form_FORM_ID_alter() and before
 * hook_form_alter().
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
 *
 * @see hook_form_FORM_ID_alter()
 * @see drupal_prepare_form()
 */
function hook_form_BASE_FORM_ID_alter(&$form, &$form_state, $form_id) {
  // Modification for the form with the given BASE_FORM_ID goes here. For
  // example, if BASE_FORM_ID is "node_form", this code would run on every
  // node form, regardless of node type.

  // Add a checkbox to the node form about agreeing to terms of use.
  $form['terms_of_use'] = array(
    '#type' => 'checkbox',
    '#title' => t("I agree with the website's terms and conditions."),
    '#required' => TRUE,
  );
}

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/**
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 * Map form_ids to form builder functions.
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 *
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 * By default, when drupal_get_form() is called, the system will look for a
 * function with the same name as the form ID, and use that function to build
 * the form. This hook allows you to override that behavior in two ways.
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 *
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 * First, you can use this hook to tell the form system to use a different
 * function to build certain forms in your module; this is often used to define
 * a form "factory" function that is used to build several similar forms. In
 * this case, your hook implementation will likely ignore all of the input
 * arguments. See node_forms() for an example of this.
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 *
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 * Second, you could use this hook to define how to build a form with a
 * dynamically-generated form ID. In this case, you would need to verify that
 * the $form_id input matched your module's format for dynamically-generated
 * form IDs, and if so, act appropriately.
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 *
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 * @param $form_id
 *   The unique string identifying the desired form.
 * @param $args
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 *   An array containing the original arguments provided to drupal_get_form()
 *   or drupal_form_submit(). These are always passed to the form builder and
 *   do not have to be specified manually in 'callback arguments'.
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 *
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 * @return
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 *   An associative array whose keys define form_ids and whose values are an
 *   associative array defining the following keys:
 *   - callback: The name of the form builder function to invoke.
 *   - callback arguments: (optional) Additional arguments to pass to the
 *     function defined in 'callback', which are prepended to $args.
 *   - wrapper_callback: (optional) The name of a form builder function to
 *     invoke before the form builder defined in 'callback' is invoked. This
 *     wrapper callback may prepopulate the $form array with form elements,
 *     which will then be already contained in the $form that is passed on to
 *     the form builder defined in 'callback'. For example, a wrapper callback
 *     could setup wizard-alike form buttons that are the same for a variety of
 *     forms that belong to the wizard, which all share the same wrapper
 *     callback.
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 */
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function hook_forms($form_id, $args) {
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  // Simply reroute the (non-existing) $form_id 'mymodule_first_form' to
  // 'mymodule_main_form'.
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  $forms['mymodule_first_form'] = array(
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    'callback' => 'mymodule_main_form',
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  );
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  // Reroute the $form_id and prepend an additional argument that gets passed to
  // the 'mymodule_main_form' form builder function.
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  $forms['mymodule_second_form'] = array(
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    'callback' => 'mymodule_main_form',
    'callback arguments' => array('some parameter'),
  );

  // Reroute the $form_id, but invoke the form builder function
  // 'mymodule_main_form_wrapper' first, so we can prepopulate the $form array
  // that is passed to the actual form builder 'mymodule_main_form'.
  $forms['mymodule_wrapped_form'] = array(
    'callback' => 'mymodule_main_form',
    'wrapper_callback' => 'mymodule_main_form_wrapper',
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  );
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  return $forms;
}

/**
 * Perform setup tasks. See also, hook_init.
 *
 * This hook is run at the beginning of the page request. It is typically
 * used to set up global parameters which are needed later in the request.
 *
 * Only use this hook if your code must run even for cached page views.This hook
 * is called before modules or most include files are loaded into memory.
 * It happens while Drupal is still in bootstrap mode.
 */
function hook_boot() {
  // we need user_access() in the shutdown function. make sure it gets loaded
  drupal_load('module', 'user');