When repositioning, a meta-key (such as Shift) is often used to constrain the drag to a single dimension (either horizontal or vertical). This type of drag is called a constrained drag.

• 当调整位置时，元键常常被用来限制拖动在一维上进行（水平或者垂直方向），这种类型的拖动叫做“约束拖动”。