docs: def parse_option(self, option, block_name, *values):
          """ Parse options for play, end_play, and timer_play.
              """
  
          if len(values) != 1:
              raise TypeError
          value = os.path.realpath(os.path.expanduser(values[0]))
  
          if not os.path.isfile(value) and not os.path.islink(value):
              raise ValueError(u'Sound file "{0}" does not exist'
                               .format(value))
  
          # special extension check for aplay player
          ext = os.path.splitext(value)[1].lower()
          if ext != 'wav' and self._get_external_player() == 'aplay':
              raise ValueError(u"Only WAV sound file "
                               "supported for 'aplay'")
  
          if option == 'play':
              option = 'start_' + option
  
          key = option.split('_', 1)[0]
          self.files[key] = value