code: def calculate_input(self, buffer):
          
          if TriggerMode.ABBREVIATION in self.modes and self.backspace:
              if self._should_trigger_abbreviation(buffer):
                  if self.immediate:
                      return len(self._get_trigger_abbreviation(buffer))
                  else:
                      return len(self._get_trigger_abbreviation(buffer)) + 1
  
          if self.parent is not None:
              return self.parent.calculate_input(buffer)
  
          return 0
docs: Calculate how many keystrokes were used in triggering this folder (if applicable).