In my mind, the 'scalar' applies to the result of the slice, but obviously it 'reaches into' the subscripting square brackets to create a slice of the rightmost subscript.

That is what I wished happened. If I'd bothered to try to design what it should do rather than throw together the quickest patch possible, I would have made it do that (at least the me of today would have).

But, no, that isn't actually what happens. You can see that easily enough:

my @a= ('a'..'d');
my @b= (4,2,1);
print scalar @a[0,@b], $/;
print @a[scalar(0,@b)], $/;
__END__
b # $a[1] because $b[-1] is 1
d # $a[3] because @b has 3 elements
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