docs: function xpathCollectDescendants(nodelist, node, opt_tagName) {
    if (opt_tagName && node.getElementsByTagName) {
      copyArray(nodelist, node.getElementsByTagName(opt_tagName));
      return;
    }
    for (var n = node.firstChild; n; n = n.nextSibling) {
      nodelist.push(n);
      xpathCollectDescendants(nodelist, n);
    }
  }