text: public Explanation idfExplain(CollectionStatistics collectionStats, TermStatistics termStats) {final long df = termStats.docFreq();final long docCount = collectionStats.docCount();final float idf = idf(df, docCount);return Explanation.match(idf, "idf(docFreq, docCount)",Explanation.match(df, "docFreq, number of documents containing term"),Explanation.match(docCount, "docCount, total number of documents with field"));}