This appears to be an attempt to combine the best of SQL, XSLT, and various tag libraries and I think Schematron. It looks like an attempt at the Unified Theory of Markup. Much of the positives of it appear to be moving the validation (especially Schematron-like) earlier in the process. Since Schematron is run after the document has been validated an invalid structure can make it through the first validation. With Active Tags that isn’t possible. I like that idea.
I have to echo a questioner “how is this different than XSL” or the other technologies mentioned? I think what he is thinking is that it isn’t greatly different but that it combines a bunch of technologies. All in all, even if this isn’t needed and drops by the wayside, I think this guy really seems to understand XML. I’m impressed that he did the work to create such and thing and then subjected himself to the ender mercies of the Extreme audience.
“It is a way to do medium-sized things fast”.