get sectionRowIndex() {
        var nl = this.parentNode.getElementsByTagName(this.tagName);
        for (var i=0; i<nl.length; i++) {
            if (nl[i] === this) {
                return i;
            }
        }
        return -1;
    }
http://dev.w3.org/html5/spec/Overview.html#dom-tr-sectionrowindex