Every descriptor has an Optional option that is set to either false (the default) or true. You can see this option as a listbox below the Number of Fields input field in Figure 1. The macro language uses the optional attribute of the descriptor element to store this option

The Optional option states how a individual descriptor's result is to be treated when the macro runtime uses the default combining rule to combine the boolean results of the descriptors. By default this option is set to false, signifying that the descriptor's result is required rather than optional.