Advanced approaches to XML document validation
The Relaxed Project is to incorporate the best available validation tools and techniques to create a universal validation service for HTML/XHTML.
They use Relax NG and Schematron to do much of the validation…due to the simplicity of RelaxNG and the power of Schematron.
Basically things that the W3C validator allows through, their validator reports as errors (incorrect value for @color, mismatch of @name and @id, etc). Pretty sweet.
They also have a firefox extension…jeeze this is the most ready for prime time thing so far. Tommie really was right about the bleeding edge ideas that aren’t ready for prime time and this item which I will be running all my websites against in the future.