sorry, is There a Guide?? Why dnn's creator don't resolve this problem?

A couple of comments: 

1.  We are working on XHTML compliance and expect to be one step closer in the 4.7 release.  However, just because the core platform is compliant doesn't mean your website will be compliant.  That is up to you and the modules you choose to use.

2.  I have heard lots of developers talk about compliance in the last couple of years, but few are able to articulate a reason why this is important.  But just because a bunch of computer geeks think something is great, doesn't mean the end user cares about that feature.  Compliance is a totally arbitrary designation since it means different things to different people.  Should I be WCAG 1.0 compliant?  Section 508 compliant?  Compliant with HTML 4.01 or XHTML 1.0?  CSS 1.0 or CSS 2.0?  People may disagree, but I don't know of anybody who has visited a site and then went somewhere else because the site designers used a table or they used a mozilla only CSS property.  When designing sites I look first and formost at whether it supplies the information that my target audience is seeking and whether it does so that is accessible to my audience.  Yes I try to take accessibility into account, but if you read the standards you find that many of them are very flexible about what is required versus what is recommended.  One thing I always keep in mind is the cost of "compliance" versus the benefit. 

Project specs don't normally ask for W3C complaince, they expect Sec 508 and other access legislation compliance.  And it's not DNN, it's your skin and your content, including the modules you use.

Jeff