| GB_WATCH_CALLBACK | Watch callback function. |
| GB_WATCH_NONE | Constant to stop watching. |
| GB_WATCH_READ | Constant to watch for reading. |
| GB_WATCH_READ_WRITE | Constant to watch for both reading and writing. |
| GB_WATCH_WRITE | Constant to watch for writing. |
| GB.Watch | Starts or stops watching a file descriptor |