[Minor Change Proposal] Allow back reference with nest level in Oniguruma for Ruby again

Remark: I posted this text in comp.lang.ruby first, but Matz told me, 
that this here will be the better place. Now the Text:

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...

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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>
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...and in the Oniguruma description...

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  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
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This feature disapeared for Ruby later on...

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2006/08/11: Version 4.2.3

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