WindowClickSelect is a notebook option that specifies whether the window for the notebook should become selected if you click it.
WindowOpacity is a notebook option that determines the overall opacity of a displayed window.
$AssertFunction specifies a function to apply to assertions that fail.
$DisplayFunction gives the default setting for the option DisplayFunction in graphics functions.
There will probably be times when you want to stop Mathematica in the middle of a calculation. Perhaps you realize that you asked Mathematica to do the wrong thing. Or ...
void UTF8String_disown (char*s) disowns a string argument.
ExposeWidgetReferences is an option to Widget which specifies a list of normally internal \:f3b5children widget reference names to include as publicly available instances.
Sinusoid is a type of waveform.