Source

File: wp-includes/rewrite.php

function add_permastruct( $name, $struct, $args = array() ) {
	global $wp_rewrite;

	// Back-compat for the old parameters: $with_front and $ep_mask.
	if ( ! is_array( $args ) ) {
		$args = array( 'with_front' => $args );
	}
	if ( func_num_args() == 4 ) {
		$args['ep_mask'] = func_get_arg( 3 );
	}

	$wp_rewrite->add_permastruct( $name, $struct, $args );
}