From: "Wolfgang Nádasi-Donner" <wonado@...>
Date: 2007-05-15T05:20:08+09:00
Subject: [Minor Change Proposal]Allow back reference with nest level in Oniguruma for Ruby again

Hello dear Ruby folks!

Nearly one year ago I asked K. Kosako for a new Oniguruma feature which will 
help to recognize plindrome sentences. It was an idea for an article series in 
Ruby-Mine, a german Ruby blog site, about pattern matching with Ruby using 
regular expressions.

K. Kosako built a special new element, which is described in the History...

-----------------------------------------------------------------
2006/07/18: Version 4.2.0

2006/07/18: [test] success in ruby 1.9.0 (2006-03-01) [i686-linux].
2006/07/18: [new]  (thanks Wolfgang Nadasi-Donner)
                    add back reference with nest level.
                    \k<name+n>, \k<name-n>
-----------------------------------------------------------------

...and in the Oniguruma description...

-----------------------------------------------------------------
   back reference with nest level

     \k<name+n>     n: 0, 1, 2, ...
     \k<name-n>     n: 0, 1, 2, ...
     \k'name+n'     n: 0, 1, 2, ...
     \k'name-n'     n: 0, 1, 2, ...

     Destinate relative nest level from back reference position.

     ex 1.

       /\A(?<a>|.|(?:(?<b>.)\g<a>\k<b+0>))\z/.match("reer")

     ex 2.

       r = Regexp.compile(<<'__REGEXP__'.strip, Regexp::EXTENDED)
       (?<element> \g<stag> \g<content>* \g<etag> ){0}
       (?<stag> < \g<name> \s* > ){0}
       (?<name> [a-zA-Z_:]+ ){0}
       (?<content> [^<&]+ (\g<element> | [^<&]+)* ){0}
       (?<etag> </ \k<name+1> >){0}
       \g<element>
       __REGEXP__

       p r.match('<foo>f<bar>bbb</bar>f</foo>').captures
-----------------------------------------------------------------

This feature disapeared for Ruby later on...

-----------------------------------------------------------------
2006/08/11: Version 4.2.3

...
2006/08/07: [spec] move definition of USE_BACKREF_AT_LEVEL into NOT_RUBY.
-----------------------------------------------------------------

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
My question is now - WHY?????

I would like to see it workable for Ruby again, it can be useful - and - it is 
already there!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Wolfgang N�dasi-Donner