If a property value starts with "=", the following portion will be evluated as a math expression.

Ex:

=1 + 3

will display:

4

Note that queries can be used in place of actual values.  Ex:

=<r:GetRootObject.GetAllComponents(Separator:+).Price>

This query will return all component prices separated by a "+" sign.  The end result will be the sum of all component prices.

(Note: This assumes the 'Price' property exists, and is properly filled in...)