[Stefan Schmiedl]:
>> I'm not sure how much useful it is.  And I'm (little bit) afraid of it
>> might cause request for String#prev, which is way difficult to define.
> 
> IMO the *only* way to define String#prev is such that
> aString.prev.succ == aString.succ.prev == aString.

This is not enough to uniquely define String#prev. 

	"09".succ == "9".succ

// Niklas