code: def FlipLogic(self, **unused_kwargs):
      
      if hasattr(self, 'flipped') and self.flipped:
        raise errors.ParseError(
            'The operator \'not\' can only be expressed once.')
  
      if self.current_expression.args:
        raise errors.ParseError(
            'Unable to place the keyword \'not\' after an argument.')
  
      self.flipped = True
  
      # Check if this flip operation should be allowed.
      self.FlipAllowed()
  
      if hasattr(self.current_expression, 'FlipBool'):
        self.current_expression.FlipBool()
        logging.debug('Negative matching [flipping boolean logic].')
      else:
        logging.warning(
            'Unable to perform a negative match, issuing a positive one.')
docs: Flip the boolean logic of the expression.
  
      If an expression is configured to return True when the condition
      is met this logic will flip that to False, and vice versa.