== The danger of validating your XHTML

The danger of validating XHTML is that the validation is almost
certainly not doing what you believe it's doing.

The problem is that all the common online validators ignore the HTTP
Content-Type of what your web server returns when validating your page,
and use only the DOCTYPE. This is completely wrong in the case of XHTML,
because ~~browsers only treat pages as XHTML if they are served as
_application/xhtml+xml_~~. All the DOCTYPE does is let the browser decide
what sort of XHTML it has, since there are now several flavours.

(No less authority than the W3C says that
browsers should behave this way; see [[this mailing list message
http://lists.w3.org/Archives/Public/www-html/2000Sep/0024.html]], or
[[this Safari blog entry http://webkit.org/blog/?p=68]], or even the
W3C's [[XHTML media types note http://www.w3.org/TR/xhtml-media-types/]].)

So if you serve your beautifully validated XHTML as _text/html_, what
browsers will actually see it as is good old HTML tag soup. *And
validators won't tell you this*; they will happily tell you that your
_text/html_ page is valid XHTML, when an honest answer is that it is
invalid HTML.

(In [[some future world
http://www.intertwingly.net/blog/2006/12/01/The-White-Pebble]] it may
be [[valid http://www.intertwingly.net/blog/2006/12/04/Inch-by-Inch]]
[[HTML http://en.wikipedia.org/wiki/HTML5]][[5
http://annevankesteren.nl/2005/04/html5]].)

If you are merely using XHTML validation as a good housekeeping seal
of approval, you should write to HTML 4.01 Strict instead; it is just
as strong, and browsers will actually interpret your pages the way you
think they are, saving you various headaches.

If you are using XHTML validation to prepare for serving your pages
as _application/xhtml+xml_ in the future, you are probably fooling
yourself, because your pages may or may not actually work as real XHTML
(see some of the links [[here XHTMLMasochism]] for a full explanation).

If you are trying to serve real XHTML to selected browsers and your
XHTML document as HTML to Internet Explorer, and you are not using
either MathML or SVG, [[you are a masochist XHTMLMasochism]].