I've wanted string bookmarks on several occasions in Perl. It is nice that you can parse with:

    if(   /.../gc    ) {
    } elsif(  /:::/gc  ) {
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but it'd be even nicer to be able to work with substitutions in a similar manner, single-stepping different substitutions intermixed with different matches and being able to make multiple substr() LVALUE things that keep their position in the face of such substitutions or changes to other substr() LVALUE things.

                - tye