public function addNumberLexeme()
    {
        $this->_lexemes[] = new Zend_Search_Lucene_Search_QueryToken(
            Zend_Search_Lucene_Search_QueryToken::TC_NUMBER,
            $this->_currentLexeme,
            $this->_queryStringPosition - 1
        );
        $this->_currentLexeme = '';
    }