docs: def register_lookup(cls, lookup, lookup_name=None):
          """Register a Lookup to a class"""
          if lookup_name is None:
              lookup_name = lookup.lookup_name
          if 'class_lookups' not in cls.__dict__:
              cls.class_lookups = {}
  
          cls.class_lookups[lookup_name] = lookup
          cls._clear_cached_lookups()
  
          return lookup