I want to create a button that will call an external "compare" program. I need to pass the 1st and 2nd selected filenames from the lister. I know about the available codes for passing filenames but how do I specifically select the 1st and 2nd? I can't seem to find any reference to this.
Scripting already provides an easy way to do that, since scripts have access to a collection of selected files that they can index by number if they need to.
As it's fairly rare* to need it, it's probably not something we'll add to the basic codes like {filepath}.
(* Outside of comparison tools, where you probably want to use scripting anyway, to cover all the different situations like two files in the same folder, or one file one the left and another file on the right.)