code: func NewLowerCaseFilter(matchVersion util.Version, in TokenStream) *LowerCaseFilter {
  	ans := &LowerCaseFilter{
  		TokenFilter: NewTokenFilter(in),
  		input:       in,
  		charUtils:   GetCharacterUtils(matchVersion),
  	}
  	ans.termAtt = ans.Attributes().Add("CharTermAttribute").(CharTermAttribute)
  	return ans
  }
docs: /* Create a new LowerCaseFilter, that normalizes token text to lower case. */