检验浏览器是否支持未知元素的方法

(function() {
    try {
        var a = document.createElement('a');
        a.innerHTML = '<xyz></xyz>';
       //if the hidden property is implemented we can assume, that the browser supports  basic HTML5 Styles
        supportsHtml5Styles = ('hidden' in a);
        supportsUnknownElements = a.childNodes.length == 1 || (function() {
            // assign a false positive if unable to shiv
             (document.createElement)('a');
              var frag = document.createDocumentFragment();
        return (
            typeof frag.cloneNode == 'undefined' ||
            typeof frag.createDocumentFragment == 'undefined' ||
            typeof frag.createElement == 'undefined'
            );
    }());
        } catch(e) {
           // assign a false positive if detection fails => unable to shiv
            supportsHtml5Styles = true;
            supportsUnknownElements = true;
    }
}());