xml-based schema vs form.schema?

[Luke]

I've been creating dexterity types using form.schema and now that I've gotten a look at the updated documentation and plone.app.contenttypes I see its using supermodel now with schemas defined in xml.  What is the preferred method for dexterity development going forward?  I just created a behavior that works with my form.schema content, but when I apply it to a type created with XML-schema's the behavior fields aren't rendered in the edit form.  Previously I had tried to extend IDocument (from plone.app.contenttypes) by importing the interface and subclassing it.  While producing no errors, the subclassed type was also missing the schema provided by IDocument.

Regards,

Luke