Well her int he Netherlands for Dutch government projects its a guideline
As of 1 September last year, every website built for a government agency is required by law to use:
- valid HTML 4.01 or XHTML 1.0
- CSS and semantic HTML and separation of structure and presentation
- progressive enhancement
- the W3C DOM (instead of the old Microsoft
document.all)
- meaningful values of
class and id
- meaningful
alt attributes on all image
and thats not everything they go even further
Furthermore:
- scripts that work on links should extend the basic link functionality (think accessible popups)
- if a link makes no sense without a script, it shouldn't be in the HTML (but be generated by JavaScript)
- use of forms or scripts as the only means of getting certain information is prohibited
- removing the focus rectangle on links is prohibited
- information offered in a closed format (think Word) should also be offered in an open format
- the semantics of many HTML elements are explicitly defined ( meaning a lot of unordered lists, paragraphs and only tables for tabualr display of data )
You can read (in Dutch) here
http://webrichtlijnen.overheid.nl/besluit/tekst-besluit-en-toelichting/
The go very far in this and a DNN site out of the box without any modification doenst comply to a lot of the rules for validity, acessibillity and semantically correct use of html