qw(b a) is (currently) equivalent to ('b', 'a') at a very low level. The parser only sees the latter.

It also fools the x operator.

>perl -le"$,=', '; print qw( a b c ) x 3"
a, b, c, a, b, c, a, b, c

>perl -le"$,=', '; print sub { qw( a b c ) }->() x 3"
ccc
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Update: Even high level stuff like for.

>perl -le"for my $x qw( a b c ) { print $x }"
a
b
c
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