It sounds to me as though you are laboring under the false assumption that pressing <Enter> invokes some special system call, and that, for example, pressing <A> or <Spacebar> does not. Is this what you're thinking? Over-simplifying: Pressing any key simply produces a keycode. The system first looks and decides it has nothing to do with the <Enter> keycode, so it passes the keycode on to the next entity that might be interested in a key press. For simplicity, lets say that the next guy is the Window Manager. The Window Manager examines the keycode and decides that it doesn't know how to handle this key, so it passes the keycode on to the next entity that might be interested in a key press. We'll call the next entity the Focused Program. And here's where it gets interesting. The Focused Program receives the keycode and handles it by whatever context exists in the program. If the Focused Program is xterm or gnome-terminal or such then it does as you've described. If the Focused Program has a Focused Widget (a text entry or menu or whatever) then it will likely pass the keycode on to the routines that handle events for that Widget, so that the Widget becomes the context for how the key is handled. No magic. All keys are handled the same way. (With some special consideration for combination keys like <shift> or <ctrl>.) If all of this is obvious to you then I've clearly misunderstood what you're having trouble understanding. If so, sorry, move along...
