a POSIX group ID
| std_types::object | the prototype object for all "normal" objects |
| std::getgid | returns the real group ID |
| std::getegid | returns the effective group ID |
| std::equal | compares two group IDs for equality |
| std::hash | returns an integer hash value for a group ID |
| std::to_integer | returns an integer value representing the group ID |