Quoting Matthew G. Saroff (msaroff(_at_)pca(_dot_)net):
Is this [<tab><space>] or [<space><tab>]?
BTW, I've seen reference to this before, but it's not in the man
pages. What does it mean?
It means match a space or a tab. The + or * after it mean "match one
or more" or "match zero or more" of the preceeding set; i.e., any
combination of spaces and tabs. This is done because some mailers
use spaces as deliters and others use tabs.
Michael Stone, Sysadmin, ITRI
PGP: finger, or email with "Subject: get pgp key"