The ++ operator can act upon both numbers and strings in a predictable fashion. With strings, 'A' increments to 'B', and 'Z' to 'AA'. ...and so on.

The magic of the ++ operator with respect to strings also exherts itself by providing the .. operator (range operator) with similar magic.

Try this at home...

my $x = 1;
my $b = 'A';
$x++; # $x now equals 2.
$b++; # $b now equals 'B'.
my @numbers = (1..10);
  # @numbers now contains 1, 2, 3, .. 10.
my @letters = ('A'..'Z');
  # @letters now contains A, B, C, .. Z. 

my @more = ('A'..'AZ');
  # @more now contains A, B, .. Z, AA, AB, ..AZ.
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It seems that ++ magic, and .. magic, are related. Don't be fooled into expecting -- to be magic too though, it isn't. Neither can you use the .. operator alone to create descending lists.

my $b = 'Z';
$b--; # You don't get Y.

my @array = (10..1); # You don't get 10, 9..1.

my @letters = ('Z'..'A'); # You don't get the letters reversed.
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Have fun with ++ and .. but take care not to expect magic from --. -- is for numbers.