I'm guessing that (?>a*b*) is equivalent to Java's a*+b*+.

The equivalent to Java's a*+b*+ would be (?>a*)(?>b*). In this case that wouldn't make a difference of course, but it would in situations like this one:

$_ = "aaab";

print "/(?>[ab]+)(?>b+)/ matches $_\n" if /(?>[ab]+)(?>b+)/;
print "/(?>[ab]+b+)/ matches $_\n"     if /(?>[ab]+b+)/;
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What about (?>a*(b|c)d*)? Can that be expressed in Java at all?

How about (a*(b|c)d*){1}+? (Yeah, it's ugly...)

— Arien