Kills WordPress execution and displays Ajax response with an error message.

This is the handler for wp_die() when processing Ajax requests.

function _ajax_wp_die_handler( $message, $title = '', $args = array() ) {
	// Set default 'response' to 200 for Ajax requests.
	$args = wp_parse_args(
		$args,
		array( 'response' => 200 )
	);

	list( $message, $title, $parsed_args ) = _wp_die_process_input( $message, $title, $args );

	if ( ! headers_sent() ) {
		// This is intentional. For backward-compatibility, support passing null here.
		if ( null !== $args['response'] ) {
			status_header( $parsed_args['response'] );
		}
		nocache_headers();
	}

	if ( is_scalar( $message ) ) {
		$message = (string) $message;
	} else {
		$message = '0';
	}

	if ( $parsed_args['exit'] ) {
		die( $message );
	}

	echo $message;
}