support for captures() in expandf()

[mrabarnett]

Original report by Anonymous.

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I am doing a capture of repeating groups, for eventual substitution, and need the ability to reference specific captured values in substitutions and expansions (ie, expand/expandf).

Ideally, the format of the match expansion would be enhanced to differentiate between groups and captures, and within captures, specify an index, perhaps with a dot notation: Ie, {1.2} would match the second match of the first capture group.

[mrabarnett]

Original comment by Anonymous.

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Can you give me an example of your use-case?

[mrabarnett]

Original comment by Anonymous.

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Added in regex 2015.03.18.