AT&T test data from:
    http://www2.research.att.com/~gsf/testregex/

The above link does not exist anymore; a copy of it is maintained at:
    https://github.com/gburd/testregex

Quoting from the page:
    testregex.c 2004-05-31 is the latest source for the AT&T Research
    regression test harness for the X/Open regex pattern match interface.
    See testregex(1) for option and test input details. The source and
    test data posted here are license free.