public function addWordDelimiter($delimiter)
    {
        if (in_array($delimiter, $this->getWordDelimiters())) {
            throw new \Exception("Word delimiter '$delimiter' is already there.");
        }
        if (empty($delimiter)) {
            throw new \Exception('Word delimiter cannot be null.');
        }
        if (is_array($delimiter)) {
            $this->_wordDelimiters = array_merge($this->getWordDelimiters(), $delimiter);
        } else {
            $this->_wordDelimiters[] = $delimiter;
        }
        return $this;
    }