docs: def domain_name(self, levels=1):
          """
          Produce an Internet domain name with the specified number of
          subdomain levels.
  
          >>> domain_name()
          nichols-phillips.com
          >>> domain_name(2)
          williamson-hopkins.jackson.com
          """
          if levels < 1:
              raise ValueError("levels must be greater than or equal to 1")
          if levels == 1:
              return self.domain_word() + '.' + self.tld()
          else:
              return self.domain_word() + '.' + self.domain_name(levels - 1)