docs: def entity_tags_form(self, entity, ns=None):
          """Construct a form class with a field for tags in namespace `ns`."""
          if ns is None:
              ns = self.entity_default_ns(entity)
  
          field = TagsField(label=_l("Tags"), ns=ns)
          cls = type("EntityNSTagsForm", (_TagsForm,), {"tags": field})
          return cls