just because _YOU_ don't hear about them doesn't mean they don't exist.
they do.
however, they are seldom used.
Hmm...theres something a little peculiar here. Oh i see what it is! the sentence is talking about itself! do you see that? what do you mean? sentences can\'t talk! No, but they REFER to things, and this one refers directly-unambigeously-unmistakably-to the very sentence which it is!