Here's how I feel about proprietary features: In DOM, fine. In CSS, fine, as long as you properly follow the naming conventions for proprietary features. In XHTML, fine, as long as they're under a separate namespace. But in HTML? No. HTML is quite full of useless non-structural junk as it is; we don't need canvas elements and ping attributes. But someone in Mozilla land thinks these additions are a good idea. I very much disagree.

Recently one of the developers at Mozilla added a ping attribute to the a element. This attribute allows content authors to provide a list of servers to ping whenever the link is clicked. Totally useless, and can and should already be done via scripting. Considering that Firefox is supposed to be one of the poster boys of web standards, this is really disappointing.

Technically speaking, this isn't proprietary in the same sense as things like marquee were. It's part of the public Web Applications 1.0 working draft, which is being drawn up by the Web Hypertext Application Technology Working Group (WHATWG). But still, the World Wide Web Consortium is doing a fine job in this area and they really have the right idea about separation of content, presentation, and behavior. WHATWG clearly doesn't. The canvas element and ping attribute have no place in HTML, and I think you have to be clueless about the progress we have made in the last few years to think that these additions are a good thing. Perhaps in a different namespace, but not in HTML land.

I only partialy agree with you.
I think these special tags/attributes are very usefull, however, it would have been better to extend xhtml via a special namespace instead of building them into html.
The Browsers that will support these features or allready do are the ones that allready support *real* xhtml. IE does not support *real* xhtml and it will neither support these special features.
Adding a xhtml namespace for these features would have been way better from a sematical point of view and from the point which browsers do or will support these features.