Mouse: 
Changes the function of the mouse so that it can split an object. First, view the points of the object to be split by selecting Selected Entities’ Points from the View menu.
To split a line, click down with the left mouse button on the point at which the line is to be split. Let the mouse button back up to split the line.
To split a polygon, click down with the left mouse button on a point at which the polygon will be split. Drag the mouse clear of the first point and let the left button up. To form the splitting line, click with the left mouse button to form a polyline as many times as desired. When the mouse button is clicked within a point of the polygon, the polygon will be split along the polyline drawn. When splitting an object which contains more than one polygon, each polygon should intersect the splitting line an even number of times for the object to be split.