When you click on a the listbox field selector on the left side, at the bottom of it there is a textbox that gets the name of the field you clicked as it's value, in there you can put any expression and optionally add the AS clause
"The five senses obstruct or deform the apprehension of reality."
Jorge L. Borges?
"Premature optimization is the root of all evil in programming."
Donald Knuth, repeating C. A. R. Hoare
"To die for a religion is easier than to live it absolutely"
Jorge L. Borges
