docs: def bold(self, action):
          '''Enable/cancel bold printing
          
          Args:
              action: Enable or disable bold printing. Options are 'on' and 'off'
          Returns:
              None
          Raises:
              RuntimeError: Invalid action.
          '''
          if action =='on':
              action = 'E'
          elif action == 'off':
              action = 'F'
          else:
              raise RuntimeError('Invalid action for function bold. Options are on and off')
          self.send(chr(27)+action)