This seems to actually work: 
"aab"=~/(.)(?(?=\1)\1(*SKIP)(*FAIL)|)/

[download]
(or a mark followed by a named skip instead of the bare skip) but I'm reluctant to use it without actually feeling like I understand.

In reply to Re: understanding (*SKIP:...) by ysth
in thread understanding (*SKIP:...) by ysth

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