code: function isHtmlElement(node, tags) {
  	if (typeof tags == "string") {
  		tags = [tags];
  	}
  	if (typeof tags == "object") {
  		tags = tags.map(function(tag) { return tag.toUpperCase() });
  	}
  	return node
  		&& node.nodeType == Node.ELEMENT_NODE
  		&& isHtmlNamespace(node.namespaceURI)
  		&& (typeof tags == "undefined" || tags.indexOf(node.tagName) != -1);
  }
docs: "An HTML element is an Element whose namespace is the HTML namespace."  I allow an extra argument to more easily check whether something is a particular HTML element, like isHtmlElement(node, "OL").  It accepts arrays too, like isHtmlElement(node, ["OL", "UL"]) to check if it's an ol or ul.