SYSTEM.MOUSE_Y_POS
SYSTEM.MOUSE_Y_POS represents (as a CHAR value) the y coordinate of the mouse, using units of the current coordinate system. If the mouse is in an item, the value is relative to the upper left corner of the item's bounding box. If the mouse is on a canvas, the value is relative to the upper left corner of the canvas.
/*
** Example: See SYSTEM.MOUSE_ITEM and
** SYSTEM.MOUSE_BUTTON_SHIFT_STATE.
*/
SYSTEM.MOUSE_BUTTON_PRESSED examples
SYSTEM.MOUSE_BUTTON_SHIFT_STATE examples
SYSTEM.MOUSE_FORM system variable