[ale] Yet another regex question

[Christopher Fowler]

I'm trying to create a regex that will catch only the string 'ABCDEF'
If the string is '% ABCDEF' I do not want the POSIX regex engine to
catch.  Is there a way I can create a regex that will ignore 'ABCDEF' if
it it preceeded with a '%\s'?  The \s is a space.

Thanks,
Chris