code: func NewStopFilter(matchVersion util.Version,
  	in TokenStream, stopWords map[string]bool) *StopFilter {
  
  	ans := &StopFilter{stopWords: stopWords}
  	ans.FilteringTokenFilter = NewFilteringTokenFilter(ans, matchVersion, in)
  	ans.termAtt = ans.Attributes().Add("CharTermAttribute").(CharTermAttribute)
  	return ans
  }
docs: /*
  Constructs a filter which removes words from the input TokenStream
  that are named in the Set.
  */