bug#5393: control message for bug 5393

[Lars Ingebrigtsen]

The original suggestion was:

---

I have attached a patch that enables you to
use lookaround assertion in regexp
with following syntax:

* Positive lookahead assertion
    \(?=...\)
* Negative lookahead assertion
    \(?!...\)
* Positive lookbehind assertion
    \(?<=...\)
* Negative lookbehind assertion
    \(?<!...\)

Basically, it works as same as Perl's one.

Spec:
* Any pattern is allowed in lookahead assertion.
* Nested looaround assertion is allowed.
* Capturing is allowed only in positive lookahead/lookbehind assertion.
* Duplication is allowed after such assertion.
* Variable length pattern is NOT yet allowed in lookbehind assertion.
  [x] \(?<=[0-9]+\)MB
  [o] \(?<=[0-9][0-9][0-9][0-9]\)MB
* Lookahead assertion over start bound is not allowed in re-search-backward.
  (re-search-backward "\(?<=a\)b") for buffer "abca_|_b"
  will seek to first "ab".

---

That looks pretty cool to me, but there was next to no discussion about
this at the time (2009), which is a bit odd...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no