docs: def ein(self):
          """Generate a random United States Employer Identification Number (EIN).
  
           An United States An Employer Identification Number (EIN) is
           also known as a Federal Tax Identification Number, and is
           used to identify a business entity. EINs follow a format of a
           two-digit prefix followed by a hyphen and a seven-digit sequence:
           ##-######
  
           https://www.irs.gov/businesses/small-businesses-self-employed/employer-id-numbers
          """
  
          # Only certain EIN Prefix values are assigned:
          #
          # https://www.irs.gov/businesses/small-businesses-self-employed/how-eins-are-assigned-and-valid-ein-prefixes
  
          ein_prefix_choices = [
              '01',
              '02',
              '03',
              '04',
              '05',
              '06',
              '10',
              '11',
              '12',
              '13',
              '14',
              '15',
              '16',
              '20',
              '21',
              '22',
              '23',
              '24',
              '25',
              '26',
              '27',
              '30',
              '31',
              '32',
              '33',
              '34',
              '35',
              '36',
              '37',
              '38',
              '39',
              '40',
              '41',
              '42',
              '43',
              '44',
              '45',
              '46',
              '47',
              '48',
              '50',
              '51',
              '52',
              '53',
              '54',
              '55',
              '56',
              '57',
              '58',
              '59',
              '60',
              '61',
              '62',
              '63',
              '64',
              '65',
              '66',
              '67',
              '68',
              '71',
              '72',
              '73',
              '74',
              '75',
              '76',
              '77',
              '80',
              '81',
              '82',
              '83',
              '84',
              '85',
              '86',
              '87',
              '88',
              '90',
              '91',
              '92',
              '93',
              '94',
              '95',
              '98',
              '99']
  
          ein_prefix = random.choice(ein_prefix_choices)
          sequence = self.random_int(min=0, max=9999999)
  
          ein = "{0:s}-{1:07d}".format(ein_prefix, sequence)
          return ein