protected function getScriptJsAsync(array $tag_frag, $test_for_js = true)
    {
        if ($test_for_js && !$this->isScriptTagFragJs($tag_frag)) {
            return ''; // This script tag does not contain JavaScript.
        }
        if (preg_match('/\s(?:async|defer)(?:\>|\s+[^=]|\s*\=\s*(["\'])(?:1|on|yes|true|async|defer)\\1)/ui', $tag_frag['script_open_tag'], $_m)) {
            return 'async'; // Yes, load this asynchronously.
        } // unset($_m); // Just a little housekeeping.

        return ''; // Unable to find a TRUE `async|defer` attribute.
    }