jdMorgan - 1:51 pm on Aug 3, 2010 (gmt 0)

To avoid duplicating the slash if it is present in the requested URL-path. Using $1, if example.com/phpBB3/something was requested, you would end up with example.com/forum//something.

An alternative would be to use two rules, one for "example.com/phpBB3" requests, and another for "example.com/phpBB3/<anything or nothing>" requests, but that would be rather a waste of bytes and CPU time.

Jim