It's not really because of efficiency concerns, I would like my regexp (if possible) to work with the sadly enough more simple c regexp function in sed and grep. I'm not sure that look-behinds are supported.

I'm just learning more about regexp's, which is why I wanted to solve it without multiple lines of perl code. I'm a bit surprised that you can group several words in an or-chain, but not negate the matching of a single word without look-behind.

Not really a problem though, I'll just use look-behinds. Thanks again for your time...

   wouter