protected function _addRulesModeGnu($rules)
    {
        $ruleArray = array();

        /**
         * Options may be single alphanumeric characters.
         * Options may have a ':' which indicates a required string parameter.
         * No long options or option aliases are supported in GNU style.
         */
        preg_match_all('/([a-zA-Z0-9]:?)/', $rules, $ruleArray);
        foreach ($ruleArray[1] as $rule) {
            $r = array();
            $flag = substr($rule, 0, 1);
            if ($this->_getoptConfig[self::CONFIG_IGNORECASE]) {
                $flag = strtolower($flag);
            }
            $r['alias'][] = $flag;
            if (substr($rule, 1, 1) == ':') {
                $r['param'] = 'required';
                $r['paramType'] = 'string';
            } else {
                $r['param'] = 'none';
            }
            $this->_rules[$flag] = $r;
            $this->_ruleMap[$flag] = $flag;
        }
    }