On Oct 2, 2013, at 11:55 AM, Nicolas Goaziou <n.goaziou@gmail.com> wrote:

> Hello,
> 
> Carsten Dominik <carsten.dominik@gmail.com> writes:
> 
>> This is just a cheep way to match any character at all, because \000 should
>> not be part of any string (in C it indicates the end of a string).
>> In principle you could put any character you are sure will not turn up,
>> but \000 seems to be the safest choice.  It is
>> faster (I think) than "\\(.\\|\n\\)*" because the first will
>> just run fast and streight with a table lookup while the
>> latter need to always alternate between two alternatives.
>> I have not timed it, though.
> 
> On that topic, I would add that "^\000" must be used with care, as it
> can lead to a stack overflow in regexp matcher error quite easily. In
> particular, it may be safe to use it to match a property drawer, which
> will not be very large, but I think it's wrong to use it to match
> regular blocks or drawers, which can have arbitrary long size.
> 
> For example a regexp like "[^\000]\\." will fail when matching around
> 500 lines (72 characters long). Of course, constructs like
> "\\(.\\|\n\\)*\\." will also fail, but my point is that it is tempting
> to use "^\000" even though a regexp may not be the correct answer to the
> problem.

Yes, I agree.  This is why the real matching Org does is first looking for
 a begin line, and then for the END line, in two independent searches.
Much better and safer.

- Carsten