a #GPollFD structure holding information about a file descriptor to watch.
the priority for this file descriptor which should be the same as the priority used for glib.source.Source.attach to ensure that the file descriptor is polled whenever the results may be needed.
Adds a file descriptor to the set of file descriptors polled for this context. This will very seldom be used directly. Instead a typical event source will use glib.source.Source.addUnixFd instead.