Won't the second example capture the wrong backreferences though?

I don't see any backreferences.

I don't see a problem. The first capture will be assigned to undef (i.e. dropped), the second will be assigned to $extension, the third will be assigned to $name.

As for the parens, I guess you're right; that will just force it into an array context unnecessarily, no?

I meant the parens around \s. It was like doing $z=($x)+($y); instead of $z=$x+$y;