Backward running version look-behinds

Nozomu Katō noz.ka at
Fri Dec 11 18:17:00 UTC 2015

That is one of my ongoing works. I have been studying such an
unambiguous spec as:

1) backreference numbers are always assigned to capturing parentheses
   left-to-right, even in lookbehinds. For example,
     ["d", "ab", "a", "b", "c"].

2) A backrefernce can refer to the corresponding capturing parenthesis
   if the former occurs to the left of the latter, when both they exist
   in the same lookbehind.

These are based on the behaviours of .NET's lookbehinds. However, I am
unsure if we have already got a spec that works completely, in
particular, even when lookarounds, capturing parentheses, and
backreferences nest each other.

There is also a compact version, which is similar to Claude's spec:


On Fri, 11 Dec 2015 17:46:28 +0000, Yang Guo wrote:
> The newly proposed regexp features are mostly self-contained. Does it make
> sense to bundle them? I'm curious what the benefit of that might be.
> Yang
> On Fri, Dec 11, 2015, 18:34 Gorkem Yakin wrote:
>> At the November TC39 meeting, it was agreed that the new RegExp proposals
>> would advance together, hence it's at stage 0.
>> As for the spec text, Nozomu has something written up [1], but I haven't
>> had the time to review it yet.
>> Gorkem
>> [1]

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