The optional format attribute is set to an Attribute Value Template that dictates the output format for the number. You can use any the following choices:
| Format | Output Sequence |
|---|---|
| 1 | 1 1 2 3 4 ... 10 11 12 ... |
| 01 | 01 02 03 04 ... 10 11 12 ... |
| a | a b c ... z aa ab ac ... |
| A | A B C ... Z AA AB AC ... |
| i | i ii iii iv v vi vii viii ix x ... |
| I | I II II IV V VI VII VIII IX X ... |