On 19/01/06, Eric Luo <eric.wenbl / gmail.com> wrote: > In your solution: > > <SNPB> <foo SNPB> <SNPB bar> <foo SNPB bar> matched. > > But "STR bla SNPB " will also be matched, which is not expected. > > I really appreciate your help. Thanks > Then the lookbehind assertion would not have worked either. (?<!A)B says "Match any B that is not *immediately* preceded by an A. Regards, Stefan