docs: def ean_13(name=None):
      """
      Creates the grammar for an EAN 13 code.
  
      These are the codes on thirteen digits barcodes.
  
      :param name: name for the field
      :return: grammar for an EAN 13 field
      """
  
      if name is None:
          name = 'EAN 13 Field'
  
      field = basic.numeric(13)
  
      field = field.setName(name)
  
      return field.setResultsName('ean_13')