2. It makes sense to map a control like this to
unbounded movement in some direction ( like zoom), or movement within data that loops back on itself.
将这种控件映射为某个方向的无限制移动（如缩放），或者在数据的移动中依赖其自身才能返回才是有意义的。
3. Unfortunately, the edit window portion of this control is
unbounded, leaving users free to ter values that are out of bounds or even unintelligible garbage.
遗憾的是，这个控件的编辑窗口部分是无界的。允许用户自由输入界限以外的值，甚至是莫名其妙的垃圾。
