I thought that auto-incremement on characters would following the ASCII table. But, ord("0") is 48 and ord("1") is 49. ord("9") is 57 and chr(58) is ':'. Could someone explain what I'm not seeing? The magical auto-increment does not use the whole ASCII table. It is limited to the 10 numbers, the 26 upper-case letters, and the 26 lower-case letters.

Furthermore, as said in the Camel book (page 91), the string must match /[a-zA-Z]*[0-9]*$/. That is, you can auto-increment file or file01, but not file01a.

Anyhow, you cannot get a : as the result of auto-increment, magical or not.