Here's where my branch ran into problems w/ iterating over all fields v locally defined ones. @cahrens feels strongly that only locally defined fields not ones from mixins should be 'editable' and it's the responsibility of the xblock developer to ensure all such fields are defined directly v in the old namespaces, but, of course, none are really direct. Several existing tests failed when my code iterated over all fields v just local ones. How did you get the tests to pass?