an example can be found on AMOSPro_Examples:Examples/H-5/Help_50.AMOS
Checks if the user has clicked on the mouse buttons. The result is returned in the form of a bit pattern.
Bit 0: Set to one if the left button has been pressed. Normally zero.
Bit 1: If the Right button has ben pressed, you'll get a one in this
position. Otherwise, zero.
After the mouse has been tested, the bits are automatically reset to zero. So you can only use this command to check for a SINGLE click.
Use the MOUSE KEY function if you want to test the status continuously.