Let's go 0-based and make $0 =:= $/ so that $/ is all the parens.
Our old $0 (P5's $&) could be $<> instead, short for $<MATCH> or some such.
According to the new capture semantics document posted earlier this week:
A successful match returns a C<Match> object whose ... string value is the complete substring that was matched by the entire rule...
So the old $0 is just ~$/