Most UI decisions assume the user has a full keyboard, a mouse, and a touchscreen to work with. I didn't really think about what happens when none of that is true until I started getting messages about my Morse code translator from a different kind of user than I'd designed for — people using assistive switches, where the entire available input is a single short-press or long-press. That constraint turned out to be a genuinely interesting design problem, and it changed how I think about input...