When focussed: (default) The value changes when the control has the focus and the wheel is pointing at the control and gets scrolled. Always: The value changes when the wheel is pointing at the control and gets scrolled, no matter which control has the focus.
设置该值是否在用户滚动鼠标滚轮时发生更改。“从不”：该值不发生任何更改。“在获取焦点时”：（默认）当控件具有焦点，同时滚轮指向控件并滚动时，该值发生更改。“始终”：无论控件是否具有焦点，当滚轮指向控件并滚动时，该值都发生更改。