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callback: the callback is invoked when the activity occurs. Every time period
Whenever activity occurs the callback will be invoked and pass back a boolean value. The boolean value will be true if activity has occurred in the last period and false if no activity has occurred. If additional activity occurs within the period given by the 'throttle', then the callback will be invoked at time: X + throttle (where X is the time of last activity report send). This prevents flooding the API with activity reports. Activity is defined as keyboard or mouse interaction anywhere in the OS.
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