Type-Ahead and Auto-Repeat
If the user types when the computer is unable to process the keystrokes immediately or types more quickly than the computer can handle, the extra keystrokes are queued for later processing. This queuing is called type-ahead. There's a limit (varying with the computer) to the number of keystrokes that can be queued, but this limit is usually not reached unless the user types while the application is performing a lengthy operation.
When a character key is held down for a certain amount of time, it starts repeating automatically. This feature is called auto-repeat. The user can set the delay and the rate of repetition with the Keyboard control panel. An application can tell whether a series of keystrokes was generated by auto-repeat or by the same key being pressed several times. Your application can choose to disregard keystrokes generated by auto-repeat; this is usually a good idea for menu commands chosen with keyboard equivalents such as Command-character key combinations. Be judicious in ignoring these sequences because users can find them useful in certain situations.
In general, if the user holds down a modifier key, it has the same effect as if the user presses it once. If the user holds down a modifier key and a character key at the same time, the effect is the same as if the user holds down the modifier key while pressing the character key repeatedly.
Auto-repeat does not function during type-ahead. It operates only when the application is ready to accept keyboard input.
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