Quasimodes
Quasimodes, as Jef Raskin calls them, are modes that are temporary and exist only as long as the user explicitly keeps them active. In Inside Macintosh [Ros86], Rose calls them spring-loaded modes. The quasimodal counterpart to the Caps Lock key is the Shift key. Instead of putting the computer into a permanent mode, the Shift key introduces a transient mode that is active only as long as the user holds the key down. Since the user has to keep the quasimode alive explicitly, there is no chance that the mode will be nonobvious, unexpected, or hard to leave.
Another quasimode that Rose mentions in her book is pressing down on the mouse key; it’s active only as long as the user keeps pressing. Computers behave differently when the mouse ...
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