I don't like the idea of leftmost-outermost. That would severely slow the regex engine up if it has to decide whether it should store this capture or not each time it encounters one.

Presumably this would be resolved at the compile time of the regex, and IMO would be quite simple to resolve.

Assigning them directly to where I want them seems simpler and more reliable to me.

Hmm. I see your point (sort of) but I wonder how your angle would work with using qr// multiple times. For (not such a great) instance:

my $sep=qr/(?<sep>[-\/\\])/; 
my $date=qr/(?<year>\d{4})$sep(?<month>\d{2})$sep(?<day>\d{2})/
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Hence the reason I thought of a hash of arrays. Also, the embedded $var name would _totally_ violate the quoting rules of perl, perhaps the idea that the names map to lexicals in scope (if defined) otherwise to ones it defines itself? (Which incidentally turns regex LHS's into a variant of a my(). I really dont see how this would work without seriously changing things. Mapping to a hash wouldn't have anywhere near the number of bizarre sideffects.