Expressions are recognizable by the ‘=’ in front of the value in the Property tab e.g. a property value of ‘1+1’ will result in ‘1+1’ at runtime while ‘=1+1’ will result in ‘2’. It works like Excel except that expressions are only resolved at runtime.
Selecting a value in scope will automatically insert an expression referencing that value. There is also an Expression Editor available in the dropdown of dynamic property values where more complex expressions can be constructed.