Look-behind proposal

[Nozomu Katō]

>>> * the `s`, or `.dotall` flag: the dot `.` matches every character,
>>> including newlines;
>>> * true support of Unicode, namely: escape sequences such as `\Lu`
>>> for uppercase letter, or `\X` for grapheme cluster.
>> 
>> Why not submit proposals for these?
>> 
> 
> You are right, but procrastination and other activities... 
> But I'll try to write some more concrete proposals for those ideas.

Unlike Perl, there is no special treatment for ] that appears just after
[ or [^ in RegExp of ECMAScript. Thanks to this, [^] can be used for
what matches every character including newlines.