In the Mouse-over Stack Viewer I have a "Summary text above pieces" that reads:

$sum(Steps)$

and shows the total number of Steps in the stack.

But I cannot figure out how to convert it into a beanshell expression so I can perform some operations (I would like to substract another property). For example:

{sum(Steps)}

doesn't work. I cannot find the answer in the documentation, or what is different about this field (if there is any difference).

Of course if I type:

$sum(Steps)$ - $sum(Detachments)$

I get "8 - 3" and the player must do the math. How could I have "5" instead?