Lots of talk about microformats going on. Thats good.
Some folks worrying about the complexity of validating documents that use microformats.
Folks. All you need is some pipeline goodness.
Step 1 - get yourself an XML pipeline execution infrastructure or roll your own. Its not hard.
Step 2 - Create a two stage pipeline for validation. Stage 1 : a transform that turns class attributes into element type names. Stage 2 : a standard element-centric validation using RNC/G, DTD or XSD.