'89999'.succ # => "90000"
'nzzzz'.succ # => "oaaaa"
'Zzz'.succ # => "AAaa"
'z'.succ # => "aa"
'aa'.succ # => "ab"
'zz'.succ # => "aaa"
'AA'.succ # => "AB"
'AZ'.succ # => "BA"
'ZZ'.succ # => "AAA"
'aZ'.succ # => "bA"
'Zz'.succ # => "AAa"
'foo19'.succ # => "foo20"
'foo99'.succ # => "fop00"
'99'.succ # => "100"
'9Z99'.succ # => "10A00"
'10-99'.succ # => "11-00"
'a-a'.succ # => "a-b"
'z-z'.succ # => "aa-a"
'Hello!'.succ # => "Hellp!"
%q{'zz'}.succ # => "'aaa'"
%q{z'zz'}.succ # => "aa'aa'"
'$$$$'.succ # => "$$$%"