Defines how much the document will be scrolled when the user turns a mouse wheel.
property WheelStep: Integer;
If set to 0, the control ignores mouse wheel messages (they will be sent to the parent control).
Mouse wheel scrolling in TRVScroller depends on the system settings. The system suggests the default scrolling speed. If the suggested value is "one page", this property is ignored (if nonzero). If the suggested value is "no scrolling", no scrolling occurs. Otherwise, the component is scrolled by Round(VSmallStep*WheelStep*suggested/3) pixels.