code: def get_backspace_count(self, buffer):
          
          if TriggerMode.ABBREVIATION in self.modes and self.backspace:
              if self._should_trigger_abbreviation(buffer):
                  abbr = self._get_trigger_abbreviation(buffer)
                  stringBefore, typedAbbr, stringAfter = self._partition_input(buffer, abbr)
                  return len(abbr) + len(stringAfter)
  
          if self.parent is not None:
              return self.parent.get_backspace_count(buffer)
  
          return 0
docs: Given the input buffer, calculate how many backspaces are needed to erase the text
          that triggered this folder.