From Creatures Wikia
Syntax: IMSK mask (int)
|Bit||Event||Script number||Script details|
|1||Key down||73||_P1_ contains keycode.|
|2||Key up||74||_P1_ contains keycode.|
|4||Mouse move||75||_P1_ and _P2_ contain new x and y positions, respectively.|
|8||Mouse down||76||_P1_ contains mouse button: 1 left, 2 right, 4 middle.|
|16||Mouse up||77||_P1_ contains mouse button, as above.|
|32||Mouse wheel||78||_P1_ contains scroll amount: 120 per wheel-click.|
|64||Translated character||79||On some systems (where ideographic languages are used, for instance) keypresses do not correspond to characters. In this case the translated character is sent in _P1_ to this script.|
If, once IMSK is set, any events the agent is interested in actually occur, the agent's script 73 to 79 is called (with parameters), depending on the exact event.
Returns, as an integer, the current input event mask of TARG.
It is usually easier not to use IMSK for text input. See PAT: TEXT.