code: func (ss *IndexSearcher) searchWSI(w Weight, after *ScoreDoc, nDocs int) TopDocs {
  	// TODO support concurrent search
  	return ss.searchLWSI(ss.leafContexts, w, after, nDocs)
  }
docs: /** Expert: Low-level search implementation.  Finds the top <code>n</code>
   * hits for <code>query</code>, applying <code>filter</code> if non-null.
   *
   * <p>Applications should usually call {@link IndexSearcher#search(Query,int)} or
   * {@link IndexSearcher#search(Query,Filter,int)} instead.
   * @throws BooleanQuery.TooManyClauses If a query would exceed
   *         {@link BooleanQuery#getMaxClauseCount()} clauses.
   */