public function addField($field, $title, array $rules = array()) {
        $this->_fields[$field] = $title;

        /**
         * 0 => rule
         * rule => [opt, ...]
         */
        if ($rules) {
            foreach ($rules as $rule => $options) {
                if (is_numeric($rule)) {
                    $rule = $options;
                    $options = array();
                }

                $this->addRule($field, $rule, null, $options);
            }
        }

        return $this;
    }