Modifier state, normalised so one table serves both platforms. Primary is the "command" modifier: Ctrl on Windows and Linux, Cmd on macOS. That is the one almost every shortcut wants, and normalising it here is what removes the isMac conditionals that used to be written out by hand at every binding site. Secondary is whichever of the two is left over. It exists for exactly one shortcut - macOS full screen is Cmd+Ctrl+F - and should stay that rare.