I’m not sure if charset is required for either, but I think it’ll at least throw a warning…

Otherwise, the minimum markup for an XHTML 1 Strict document is:

And the minimum for an HTML5 document:

Not exactly related, but worth pointing out is one feature of HTML5 that seems to be in some dispute (I mentioned this on stackoverflow.com recently, and it was contested by a couple regs): in HTML5 you can nest block level elements within anchors. In XHTML you cannot.

The following line is valid HTML5, invalid XHTML:

I’ve had dozens of designs come to me with complex content that should be “clickable” (per the designer) – previously, I’d laboriously wrap each piece of layout in it’s own anchor – now, you can wrap the whole thing in one.