Your use case step labeling approach?

[Pascal]

I'd like to label the steps in my use cases' basic path, so that I can refer them from the alternate scenario's. I was wondering what you guys find the best labeling scheme.

Numerous people seem to use the sequential numbering scheme with increments of 1:
 1. Actor does A
 2. System replies B
 3. Actor does C
 4. ...

Inserting a step in this scenario leads to a renumbering nightmare, especially when you have quite a few alternate scenario's. A solution would be not to number sequentially, but arbitrary (only when needed for referral from the alternate scenario):
 - Actor does A
 1. System replies B
 2. Actor does C
 - ...

Inserting a step between 1 and 2 then yields:
 - Actor does A
 1. System replies B
 3. System asks D
 2. Actor does C
 - ...

Conceptually I think this is the best, but I think that users have a hard time understanding the logic behind this. Other options are using logical step names instead of numbers. I think that this clouds up the scenario description too much. Last but not least seems to me the old "Basic programming language" approach: number sequentially with increments of 10:
 10. Actor does A
 20. System replies B
 30. Actor does C
 40. ...

This leaves room for 9 inserts between all initial steps, e.g.:
 10. Actor does A
 20. System replies B
 25. System asks D
 30. Actor does C
 40. ...

Anyone care to share his use case step labeling approach?

Pascal.

[Kevin Brennan]

Any approach other than the first strikes me as likely to confuse non-technical users quite badly. I'd suggest that you consider instead Bittner's approach, where you give a name in brackets to the extension point where an alternate scenario can occur:

 1. Actor does A
 2. System replies B
 {Extnesion Point}
 3. Actor does C
 4. ...

If at {Extension Point} Actor does X, then System replies E}.