Suppose I have DO command: @runonce:CommandA
CommandB @runonce:CommandC
If no files are selected, all is simple- CommandA is run once, then CommandC, and CommandB is never executed.
But what happens when there are some files are selected?
Is it run CommandA, then CommandC, then CommanB once for every file selected?
Why not simply try it and find out? That's what I'd do. Using a DOS button with Echo commands or similar is usually a good bet (though there can be differences between how DOS and normal buttons work).