Zeldman points out something many Web builders (myself included) have missed: most of DOCTYPEs being included in today’s Web sites are wrong. The reason? They don’t include the full URLs.

(The current generation of browsers, though, seem to revert to “strict mode” even with the DOCTYPEs using relative URLs.)

So if you build Web sites, read Zeldman’s article in A List Apart and fix your Web building software. You’ll save yourself some headaches in the future.