C# Класс org.apache.lucene.analysis.miscellaneous.KeywordRepeatFilter
This TokenFilter emits each incoming token twice once as keyword and once non-keyword, in other words once with KeywordAttribute#setKeyword(boolean) set to true and once set to false. This is useful if used with a stem filter that respects the KeywordAttribute to index the stemmed and the un-stemmed version of a term into the same field.