Increment (++) and decrement (--) strings in Perl

Question

With perl -e \'$string=\"a\";print ++$string;\' we get b,
but with perl -e \'$string=\"b\";print --$string;\' we get -1

Answer 1

Perl give us lots of facilities, why not this one?

Because it is not intuitive what values should precede the "lowest" character in range. It may make sense that "A" + 1 should be "B", and that "B" + 1 should be "C". And therefore "B" - 1 should be "A". But what should "A" - 1 be?