code: def get_user_variables(self):
          
          # 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)
          ]
docs: 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.