Not only can you set the Auto Number to be displayed in Alpha, Numeric, Alpha-Numeric and Roman Numeral Formats, you can also set an Auto Number Seed.
The Auto Number Seed can be set from the properties window for an Activity. Anything you type in this field will appear along with the Auto Number for that Activity and will be assigned to all children of that Activity as well.
For example. If I click on the Purpose and assign an Auto Number Seed of "xBML" The Auto Numbers for every Activity in that model will appear as follows. xBML 1, xBML 1.1, xBML 1.2 etc.
You can also set Auto Number Seeds for individual Legs or specific Activities.
For Example, if I click on "Activity 1" and assign an Auto Number Seed. That seed will only appear on child Activities to "Activity 1"
NOTE: After you set an Auto Number Seed in the properties window, you will need to perform a Layout
To remove the Auto Number Seed, you can either:
Highlight the Activity on which the Auto Number Seed was assigned and delete it from the properties window.
OR
Click on the Auto Number Icon in the Toolbar and select "Clear Auto Number." This will remove all Auto Number Seeds from the model.
NOTE: After you perform this action, all the Auto Numbers in the model will be removed. However, when you perform a layout, the default Auto Numbers will reappear.