re_format(7) on FreeBSD
The text 6466c9358c1c, as FreeBSD 3.5.1-RELEASE, FreeBSD 3.5-RELEASE, FreeBSD 3.4-RELEASE, FreeBSD 3.3-RELEASE, FreeBSD 3.2-RELEASE, FreeBSD 3.1-RELEASE, FreeBSD 3.0-RELEASE, FreeBSD 2.2.9-RELEASE, FreeBSD 2.2.8-RELEASE, FreeBSD 2.2.7-RELEASE, FreeBSD 2.2.6-RELEASE shipped it.
POSIX 1003.2 regular expressions