I can tell you right away what their response will be, and it is that meta extensions are an accepted way of extending HTML5 with browser-specific features, see

I can tell you right away what their response will be, and it is that meta extensions are an accepted way of extending HTML5 with browser-specific features, see: http://wiki.whatwg.org/wiki/MetaExtensions http://wiki.whatwg.org/wiki/MetaExtensions "You may add your own values to this list, which makes them legal HTML5 metadata names. We ask that you try to avoid redundancy; if someone has already defined a name that does roughly what you want, please reuse it." They will also argue that menu is intended to create toolbars and menus within a webpage, not within the browser itself - and that by using meta extensions, the IE team have implemented their browser-specific extensions in a standards-based way supported by the WHATWG. They will say that it also doesn't pollute the markup with an extension that only applies to a single browser on a single platform (which is why WHATWG developed the meta extensions). In short, pages that implement this are HTML5 compliant. Now my own opinion. The browser makers need differentiation between their products. Browser market share is as important, if not more important, than OS market share. If Microsoft want to enable websites to deeply integrate with a Windows desktop by using meta extensions, then that seems like the right place to do it. A lot of us would prefer that every browser maker simply implements the standards, but a lot of innovation in web technologies (img tag, applets, xmlhttprequest) started life as browser-specific extensions. Frowning upon, or not allowing any differentiation would remove a lot of motivation for pouring resources into browser development. As much as we might not like it, we have to deal with it - at least they put this extension in the right place with meta instead of not implementing menu properly or doing their own implementation of menu (besides, I can't think how this desktop pinning would work on for eg. OS X and Chrome - it seems something very 'active desktop' windows specific).