$x = $y || $z;       # ok
$x = ( $y || $z );   # ok (unrequired parens)
$x = $y or $z;       # XXX
$x = ( $y or $z );   # ok

##</code><code>##

$x = $y or $z;
   means
( $x = $y ) or $z;

##</code><code>##

open my $fh, '<', $qfn  or die;  # ok
open(my $fh, '<', $qfn) or die;  # ok (unrequired parens)
open my $fh, '<', $qfn  || die;  # XXX
open(my $fh, '<', $qfn) || die;  # ok

##</code><code>##

open my $fh, '<', $qfn  || die;
   means
open my $fh, '<', ( $qfn  || die );