code: func (t *Tokenizer) CorrectOffset(currentOff int) int {
  	assert2(t.Input != nil, "this tokenizer is closed")
  	if v, ok := t.Input.(CharFilterService); ok {
  		return v.CorrectOffset(currentOff)
  	}
  	return currentOff
  }
docs: /*
  Return the corrected offset. If input is a CharFilter subclass, this
  method calls CharFilter.correctOffset(), else returns currentOff.
  */