WP_Hook::add_filter( string $hook_name, callable $callback, int $priority, int $accepted_args )

Adds a callback function to a filter hook.


$hook_name string Required
The name of the filter to add the callback to.
$callback callable Required
The callback to be run when the filter is applied.
$priority int Required
The order in which the functions associated with a particular filter 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 filter.
$accepted_args int Required
The number of arguments the function accepts.

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File: wp-includes/class-wp-hook.php. View all references

public function add_filter( $hook_name, $callback, $priority, $accepted_args ) {
	$idx = _wp_filter_build_unique_id( $hook_name, $callback, $priority );

	$priority_existed = isset( $this->callbacks[ $priority ] );

	$this->callbacks[ $priority ][ $idx ] = array(
		'function'      => $callback,
		'accepted_args' => $accepted_args,

	// If we're adding a new priority to the list, put them back in sorted order.
	if ( ! $priority_existed && count( $this->callbacks ) > 1 ) {
		ksort( $this->callbacks, SORT_NUMERIC );

	if ( $this->nesting_level > 0 ) {
		$this->resort_active_iterations( $priority, $priority_existed );

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Version Description
4.7.0 Introduced.

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