Finds a pingback server URI based on the given URL.
Checks the xhtml for the rel="pingback" link and x-pingback headers. It does a check for the x-pingback headers first and returns that, if available. The check for the rel="pingback" has more overhead than just the header.
<?php discover_pingback_server_uri( $url, $deprecated ) ?>
discover_pingback_server_uri() is located in