code: def _regex_strings(self):
          
          domain = 0
          if domain not in self.domains:
              self.register_domain(domain=domain)
          return self.domains[domain]._regex_strings
docs: A property to link into IntentEngine's _regex_strings.
  
          Warning: this is only for backwards compatiblility and should not be used if you
              intend on using domains.
  
          Returns: the domains _regex_strings from its IntentEngine