code: def register_entity(self, entity_value, entity_type, alias_of=None, domain=0):
          
          if domain not in self.domains:
              self.register_domain(domain=domain)
          self.domains[domain].register_entity(entity_value=entity_value,
                                               entity_type=entity_type,
                                               alias_of=alias_of)
docs: Register an entity to be tagged in potential parse results.
  
          Args:
              entity_value(str): the value/proper name of an entity instance
                  (Ex: "The Big Bang Theory")
              entity_type(str): the type/tag of an entity instance (Ex: "Television Show")
              domain(str): a string representing the domain you wish to add the entity to