Source

File: wp-trackback.php

function trackback_response( $error = 0, $error_message = '' ) {
	header( 'Content-Type: text/xml; charset=' . get_option( 'blog_charset' ) );
	if ( $error ) {
		echo '<?xml version="1.0" encoding="utf-8"?' . ">\n";
		echo "<response>\n";
		echo "<error>1</error>\n";
		echo "<message>$error_message</message>\n";
		echo '</response>';
		die();
	} else {
		echo '<?xml version="1.0" encoding="utf-8"?' . ">\n";
		echo "<response>\n";
		echo "<error>0</error>\n";
		echo '</response>';
	}
}