Actually, it's a little more complicated than this even. Not only might HTML add more tags, but a non-standard tag might be a W3C custom element: http://www.w3.

Actually, it's a little more complicated than this even. Not only might HTML add more tags, but a non-standard tag might be a W3C custom element: http://www.w3.org/TR/custom-elements/ http://www.w3.org/TR/custom-elements/ When users gain the ability to define their own tags, you might not know which ones are driven by directives, the custom element, or both even.