[TUHS] Use of "{}" in the Shell?

[Dave Horsfall via TUHS]

A long time ago, in a Unix manpage far away, I saw a reference to "{}"
which acted similar to "()" except that it did not fork e.g. "{exit}" would
do just that :-)

Does anyone know the provenance of this Shell?  I can't seem to reproduce
it on the MacBook or the FreeBSD box here (my Penguin box is currently
dead).

Thanks.

-- Dave