Kristof Bastiaensen wrote:

> Yes, that would clarify the situation, but is it the correct
> behaviour?  I would think that (?!a)a doesn't mean the same
> character, but consecutive ones.  Because it doesn't consume
> the character, it effectively is the character 'before' the
> match (if any).  The other behaviour wouldn't make sense,
> because (?!a)b is then exactly the same as b.

I think that it's the intended behavior. Just use /(?!a).b/ if you want 
to consume the character.

Thinking about this, it is indeed possible to implement fixed-width 
look-behind -- interesting.

Regards,
Florian Gross