WAI guidelines accessibility checking hints: Yeah, the webdev toolbar for Firefox has direct links to the cynthiasays (WAI) checker and the section 508 checker along with some other useful tools so if you don’t already have it, that’s a must for

all developers. http://chrispederick.com/work/web-developer/

Apart from Cynthia, which is ok, I would strongly recommend TAW³,

which is available as an online service, a standalone version for

download and as a Firefox extension.

You will find it at http://www.tawdis.net/taw3/cms/en (taken from WSG)

The label attribute is only required on <optgroup>; it is optional on

<option>. If browsers are behaving differently when it’s used on

<option>, just remove it.

<http://www.w3.org/TR/html4/index/attributes.html> is a quick way to

check whether an attribute is required or not.

Accessibility Guidelines – http://www.w3.org/TR/WCAG10/full-checklist.html

The online validators are all still kept separate, although work on unicorn

( http://www.w3.org/QA/Tools/Unicorn/ ) is moving, if slowly. However, the

LogValidator is a server tool which includes html, xhtml, and css

validators. It can be found at http://www.w3.org/QA/Tools/LogValidator/

Yes, you can make a WordPress, Expression Engine, Textpattern, MovableType, etc. blog COMPLETELY validate. Example:

http://www.christianmontoya.com/

 

You can even make a WordPress blog (and probably the others) output valid HTML 4 instead of XHTML. Tutorial:

http://www.christianmontoya.com/2006/02/13/serve-your-weblog-as-html-401/

The boagworld blog talked about a validator that is built into firefox.  They put the link on their website.  Not sure of the episode number.  The validator provides a tick and cross as each page loads in the browser.  Probably worth a look as it provides an instance validation rather that loading details into W3C validator.