Note that the incrementation sequences are

`0..9 => 0 + carry|1 i.e 10
A..Z => A + carry|A i.e. AA
a..z => a + carry|a i.e aa
`

- bz => ca
- wrapping the z->a gives a carry to the b next in Lower a..z is c.
- Zz => AAa
- wrapping the z->a gives a carry to the Z next in Upper case A..Z is AA.
- z9 => aa0
- incrementing 9 wraps round to zero, passing a carry up to the z. Next up from z is aa
- 9z => 10
- tricked you!! - string autoincrement
*only* works on patterns matching regex `/^[a-zA-Z]*[0-9]*\z/`, this doesn't match that pattern, so treats leading number(s) as the (**numeric?**) value and increments that. 9 goes to 10 :-)

If you spot any bugs in my solutions, it's because I've deliberately left them in as an exercise for the reader! :-)

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