WvFileWatcher is a bit more interesting than WvFile: it reads to the end of a file, and then if the file grows, select() returns true and you can read more data; if the file shrinks (which presumably means it was rewritten from scratch), it starts again at the top of the file.
To think of it another way: WvFileWatcher makes select() make sense on regular files. Normally, select() is always true for a file, since all the data is always immediately available. (Note that this isn't true if your WvFile is connected to a Unix device; then select() makes sense already, and WvFileWatcher will just mess you up.)
WvFileWatcher is very seldom used except as a WvStreams test, so we won't bother to give an example here.