code: def register_regex_entity(self, regex_str, domain=0):
          
          if domain not in self.domains:
              self.register_domain(domain=domain)
          self.domains[domain].register_regex_entity(regex_str=regex_str)
docs: A regular expression making use of python named group expressions.
  
          Example: (?P<Artist>.*)
  
          Args:
              regex_str(str): a string representing a regular expression as defined above
              domain(str): a string representing the domain you wish to add the entity to