WordPress at a glance
action is not described

set_404 action-hook . WP 5.5.0

Fires after a 404 is triggered.

Usage

add_action( 'set_404', 'action_function_name_8821' );
function action_function_name_8821( $this ){
	// action...
}
$this(WP_Query)
The WP_Query instance (passed by reference).

Changelog

Since 5.5.0 Introduced.

Where the hook is called

WP_Query::set_404()
set_404
wp-includes/class-wp-query.php 1720
do_action_ref_array( 'set_404', array( $this ) );

Where in WP core the hook is used WordPress

Usage not found.