Clean up the documentation for add_filter and apply_filters.
Fixes #19203 props DrewAPicture, ericlewis git-svn-id: https://develop.svn.wordpress.org/trunk@25476 602fd350-edb4-49c9-b593-d223f7449a82
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Peter Westwood
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@ -22,47 +22,49 @@
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/**
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* Hooks a function or method to a specific filter action.
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*
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* Filters are the hooks that WordPress launches to modify text of various types
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* before adding it to the database or sending it to the browser screen. Plugins
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* can specify that one or more of its PHP functions is executed to
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* modify specific types of text at these times, using the Filter API.
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* WordPress offers filter hooks to allow plugins to modify
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* various types of internal data at runtime.
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*
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* To use the API, the following code should be used to bind a callback to the
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* filter.
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* A plugin can modify data by binding a callback to a filter hook. When the filter
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* is later applied, each bound callback is run in order of priority, and given
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* the opportunity to modify a value by returning a new value.
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*
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* The following example shows how a callback function is bound to a filter hook.
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* Note that $example is passed to the callback, (maybe) modified, then returned:
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*
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* <code>
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* function example_hook($example) { echo $example; }
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* add_filter('example_filter', 'example_hook');
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* function example_callback( $example ) {
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* // Maybe modify $example in some way
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* return $example;
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* }
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* add_filter( 'example_filter', 'example_callback' );
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* </code>
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*
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* In WordPress 1.5.1+, hooked functions can take extra arguments that are set
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* when the matching do_action() or apply_filters() call is run. The
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* $accepted_args allow for calling functions only when the number of args
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* match. Hooked functions can take extra arguments that are set when the
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* matching do_action() or apply_filters() call is run. For example, the action
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* comment_id_not_found will pass any functions that hook onto it the ID of the
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* requested comment.
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* Since WordPress 1.5.1, bound callbacks can take as many arguments as are
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* passed as parameters in the corresponding apply_filters() call. The $accepted_args
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* parameter allows for calling functions only when the number of args match.
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*
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* <strong>Note:</strong> the function will return true no matter if the
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* function was hooked fails or not. There are no checks for whether the
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* function exists beforehand and no checks to whether the <tt>$function_to_add</tt>
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* is even a string. It is up to you to take care and this is done for
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* optimization purposes, so everything is as quick as possible.
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* <strong>Note:</strong> the function will return true whether or not the callback
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* is valid. It is up to you to take care. This is done for optimization purposes,
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* so everything is as quick as possible.
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*
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* @package WordPress
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* @subpackage Plugin
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* @since 0.71
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* @global array $wp_filter Stores all of the filters added in the form of
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* wp_filter['tag']['array of priorities']['array of functions serialized']['array of ['array (functions, accepted_args)']']
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*
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* @global array $wp_filter A multidimensional array of all hooks and the callbacks hooked to them.
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* @global array $merged_filters Tracks the tags that need to be merged for later. If the hook is added, it doesn't need to run through that process.
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*
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* @param string $tag The name of the filter to hook the $function_to_add to.
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* @param callback $function_to_add The name of the function to be called when the filter is applied.
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* @param int $priority optional. Used to specify the order in which the functions associated with a particular action are executed (default: 10). Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.
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* @param int $accepted_args optional. The number of arguments the function accept (default 1).
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* @since 0.71
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*
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* @param string $tag The name of the filter to hook the $function_to_add callback to.
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* @param callback $function_to_add The callback to be run when the filter is applied.
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* @param int $priority (optional) The order in which the functions associated with a particular action are executed. Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.
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* Default 10.
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* @param int $accepted_args (optional) The number of arguments the function accepts.
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* Default 1.
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* @return boolean true
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*/
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function add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
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function add_filter( $tag, $function_to_add, $priority = 10, $accepted_args = 1 ) {
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global $wp_filter, $merged_filters;
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$idx = _wp_filter_build_unique_id($tag, $function_to_add, $priority);
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@ -114,27 +116,36 @@ function has_filter($tag, $function_to_check = false) {
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*
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* The function allows for additional arguments to be added and passed to hooks.
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* <code>
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* function example_hook($string, $arg1, $arg2)
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* {
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* //Do stuff
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* return $string;
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* // Our filter callback function
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* function example_callback( $string, $arg1, $arg2 ) {
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* // (maybe) modify $string
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* return $string;
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* }
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* $value = apply_filters('example_filter', 'filter me', 'arg1', 'arg2');
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* add_filter( 'example_filter', 'example_callback', 10, 3 );
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*
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* // Apply the filters by calling the 'example_callback' function we
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* // "hooked" to 'example_filter' using the add_filter() function above.
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* // - 'example_filter' is the filter hook $tag
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* // - 'filter me' is the value being filtered
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* // - $arg1 and $arg2 are the additional arguments passed to the callback.
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* $value = apply_filters( 'example_filter', 'filter me', $arg1, $arg2 );
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* </code>
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*
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* @package WordPress
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* @subpackage Plugin
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* @since 0.71
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* @global array $wp_filter Stores all of the filters
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* @global array $merged_filters Merges the filter hooks using this function.
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*
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* @global array $wp_filter Stores all of the filters
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* @global array $merged_filters Merges the filter hooks using this function.
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* @global array $wp_current_filter stores the list of current filters with the current one last
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*
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* @param string $tag The name of the filter hook.
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* @since 0.71
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*
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* @param string $tag The name of the filter hook.
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* @param mixed $value The value on which the filters hooked to <tt>$tag</tt> are applied on.
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* @param mixed $var,... Additional variables passed to the functions hooked to <tt>$tag</tt>.
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* @param mixed $var Additional variables passed to the functions hooked to <tt>$tag</tt>.
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* @return mixed The filtered value after all hooked functions are applied to it.
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*/
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function apply_filters($tag, $value) {
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function apply_filters( $tag, $value ) {
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global $wp_filter, $merged_filters, $wp_current_filter;
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$args = array();
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@ -708,7 +719,6 @@ function register_uninstall_hook( $file, $callback ) {
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* @uses $wp_filter Used to process all of the functions in the 'all' hook
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*
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* @param array $args The collected parameters from the hook that was called.
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* @param string $hook Optional. The hook name that was used to call the 'all' hook.
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*/
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function _wp_call_all_hook($args) {
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global $wp_filter;
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