nction(el){
        if(el.tagName === "mark" || el.tagName === "MARK"){
            [].forEach.call(el.childNodes, function(child){
                el.parentNode.insertBefore(child, el);
            });
            el.parentNode.removeChild(el);
        }else if(el.parentNode.tagName === "mark"){
            return unmarkElement(el.parentNode);
        }
        return null;
    }

    var unmarkAll = function(root){
        root = root || document;
        [].forEach.call(root.querySelectorAll("mark"), unm