trackback_url

 * @since 0.71
 *
 * @param bool $deprecated_echo Not used.
 * @return void|string Should only be used to echo the trackback URL, use get_trackback_url()
 *                     for the result instead.
 */
function trackback_url( $deprecated_echo = true ) {
	if ( true !== $deprecated_echo ) {
		_deprecated_argument(
			__FUNCTION__,
			'2.5.0',
			sprintf(
				/* translators: %s: get_trackback_url() */
				__( 'Use %s instead if you do not want the value echoed.' ),
				'<code>get_trackback_url()</code>'
			)
		);
	}