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

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Adds a callback function to a filter hook.


The name of the filter to add the callback to.
The callback to be run when the filter is applied.
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.
The number of arguments the function accepts.


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' => (int) $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 );

	$this->priorities = array_keys( $this->callbacks );

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



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