docs: def boolean(name=None):
      """
      Creates the grammar for a Boolean (B) field, accepting only 'Y' or 'N'
  
      :param name: name for the field
      :return: grammar for the flag field
      """
  
      if name is None:
          name = 'Boolean Field'
  
      # Basic field
      field = pp.Regex('[YN]')
  
      # Parse action
      field.setParseAction(lambda b: _to_boolean(b[0]))
  
      # Name
      field.setName(name)
  
      return field