code: func (t *Tokenizer) SetReader(input io.RuneReader) error {
  	assert2(input != nil, "input must not be nil")
  	assert2(t.Input == ILLEGAL_STATE_READER, "TokenStream contract violation: close() call missing")
  	t.inputPending = input
  	return nil
  }
docs: /*
  Expert: Set a new reader on the Tokenizer. Typically, an analyzer (in
  its tokenStream method) will use this to re-use a previously created
  tokenizer.
  */