用户自定义权限
请使用$this->perm()方法获取对象
默认值 array(2) ( "field_name" => string(4) "perm" "format" => array(1) ( 0 => string(9) "serialize" ) )
array(2) ( "field_name" => string(4) "perm" "format" => array(1) ( 0 => string(9) "serialize" ) )