src/Ciconia/Extension/Gfm/UrlAutoLinkExtension.php
public function processStandardUrl(Text $text)
    {
        $hashes = array();

        // escape <code>
        $text->replace('{<code>.*?</code>}m', function (Text $w) use (&$hashes) {
            $md5 = md5($w);
            $hashes[$md5] = $w;

            return "{gfm-extraction-$md5}";
        });

        $text->replace('{(?<!]\(|"|<|\[)((?:https?|ftp)://[^\'">\s]+)(?!>|\"|\])}', '<\1>');

        /** @noinspection PhpUnusedParameterInspection */
        $text->replace('/\{gfm-extraction-([0-9a-f]{32})\}/m', function (Text $w, Text $md5) use (&$hashes) {
            return $hashes[(string)$md5];
        });
    }
public function processStandardUrl(Text $text)
    {
        $hashes = array();

        // escape <code>
        $text->replace('{<code>.*?</code>}m', function (Text $w) use (&$hashes) {
            $md5 = md5($w);
            $hashes[$md5] = $w;

            return "{gfm-extraction-$md5}";
        });

        $text->replace('{(?<!]\(|"|<|\[)((?:https?|ftp)://[^\'">\s]+)(?!>|\"|\])}', '<\1>');

        /** @noinspection PhpUnusedParameterInspection */
        $text->replace('/\{gfm-extraction-([0-9a-f]{32})\}/m', function (Text $w, Text $md5) use (&$hashes) {
            return $hashes[(string)$md5];
        });
    }
Turn standard URL into markdown URL

@param Text $text