function add_keyword_group($key, $styles, $case_sensitive = true, $words = array()) {
        $words = (array) $words;
        if  (empty($words)) {
            // empty word lists mess up highlighting
            return false;
        }

        //Add the new keyword group internally
        $this->language_data['KEYWORDS'][$key] = $words;
        $this->lexic_permissions['KEYWORDS'][$key] = true;
        $this->language_data['CASE_SENSITIVE'][$key] = $case_sensitive;
        $this->language_data['STYLES']['KEYWORDS'][$key] = $styles;

        //NEW in 1.0.8, cache keyword regexp
        if ($this->parse_cache_built) {
            $this->optimize_keyword_group($key);
        }
    }