the number of pages to change the X coordinate of the DocPosition; positive increases, negative decreases
dy
the number of pages to change the Y coordinate of the DocPosition; positive increases, negative decreases
Remarks
This method does not depend on the existence of any scrollbars, but does depend on the values of DocExtentSize and ScrollSmallChange to determine a new value for DocPosition that is a "line" less than one full "page" away from the old position times the factor provided by the parameters for each direction.