I can never remember the rules of precedence, so I just remove the relevance of such considerations by using brackets to make my intentions clear:

C:\>perl -MO=Deparse,-p -e "return $x or $y"
((return $x) or $y);
-e syntax OK

C:\>perl -MO=Deparse,-p -e "return ($x or $y)"
(return ($x || $y));
-e syntax OK
[download]

Cheers,
Rob