woocommerce_email_subject_backorder filter-hook . WC 1.0

Usage

add_filter( 'woocommerce_email_subject_backorder', 'filter_function_name_6968', 10, 3 );
function filter_function_name_6968( $subject, $args, $null ){
	// filter...

	return $subject;
}

$subject

-

$args

-

$null

-

Where the hook is called

apply_filters( 'woocommerce_email_subject_backorder', $subject, $args, null ),

Where in WP core the hook is used WooCommerce