Many unix programs don't use ``extended'' regular expressions by default. See regexp(7) on Plan 9 or try egrep/grep -E under Unix.
The Plan 9 regexp library matches the old Unix egrep command.
Any regexp you'd try under Plan 9 should work with new egreps,
though not vice versa -- new egreps tend to have newfangled
additions like [:upper:] and \w and {4,6} for repetition.
Russ
