a public method to help report engines to introspect
        a template and find what data it needs and how it will be
        used
        returns a list of user variable names without starting 'py3o.

def get_user_variables(self):
        """a public method to help report engines to introspect
        a template and find what data it needs and how it will be
        used
        returns a list of user variable names without starting 'py3o.'"""
        # TODO: Check if some user fields are stored in other content_trees
        return [
            e.get('{%s}name' % e.nsmap.get('text'))[5:]
            for e in get_user_fields(self.content_trees[0], self.namespaces)
        ]