WordPress Version: 6.1
/**
* Callback to add a base URL to relative links in passed content.
*
* @since 2.7.0
* @access private
*
* @global string $_links_add_base
*
* @param string $m The matched link.
* @return string The processed link.
*/
function _links_add_base($m)
{
global $_links_add_base;
// 1 = attribute name 2 = quotation mark 3 = URL.
return $m[1] . '=' . $m[2] . ((preg_match('#^(\w{1,20}):#', $m[3], $protocol) && in_array($protocol[1], wp_allowed_protocols(), true)) ? $m[3] : WP_Http::make_absolute_url($m[3], $_links_add_base)) . $m[2];
}