[?] Closure variables in regular expressions

There are regular expression extensions that do this:


        [a-z]{1-32}


        and this


        abc{5+}


Has anyone ever seen regular expression extensions that work like this?


        [a-z]+:n %{n}


What this would do is match 1 to many from the character set 'a-z',
and store how many times it did so into n. Then, it would match only
that many of the literal '%'...


Like this:


        abc %%%


        abcdefg %%%%%%%


But not:


        abc %%


or:


        abcdefg %%%%


Any pointers to theory to suggest this would be useful or useless?
--
Quinn Tyler Jackson
http://www.qtj.net/~quinn/
[Looks like it's equivalent in power to backreferences, which can also
count matching pairs of things. -John]

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