Autonumber reset / start from certain number

[mdeliw]

Is your feature request related to a problem? Please describe.
Once autonumber is enabled, there is no option to stop autonumber.
Once autonumber is enabled, there is no option to restart autonumber from a specific value.

Describe the solution you'd like
In case of par/and or alt/else, we need an option to restart autonumber from a certain value. This is available in plantuml.

Describe alternatives you've considered
Manual numbering without use of autonumber.

Additional context
Add any other context or screenshots about the feature request here.