Ryan,
I'm mistaken.
I found the following:
A typical application for driver tags is in a model where each object contains drivers representing both fixed and variable costs. The drivers that represent fixed costs could be tagged FIXED. The drivers that represent the variable costs could be tagged VARIABLE. You can then roll up the fixed and variable costs separately. Other applications of tags: RTB/CTB/XTB (Run the Business/Change the Business/Transform the Business), Direct/Indirect, driver layers (depreciation, labor, hardware, software), resource layers (server costs, storage costs).
To assign tags to a driver, click on the Tags field and enter the tags separated by commas. The tags should be the values taken from the identifier column in the object unit table.
You can exclude drivers by placing a minus sign in front of a tag. For example, assume there is a Fixed and a Direct driver coming into Object A and you tag them accordingly. Object A's value is allocated to Object B. To pass both the Fixed and Variable values to Object B, you would enter "Fixed,Direct" in the Tags field for the Object B driver. To pass only the Fixed value to Object B, you would enter "Fixed,-Direct".
Unfortunately, I am not getting this to work as described above.