2D extents can be adjusted to modify the visibility of a datum for all views or a single selected view.
The 3D control changes to display 2D, and the control changes from an open circle to a filled circle. This means the datum is in view-specific mode. If you resize the datum, the change occurs in that view only.
View-specific extent control
If you move the 2D control of a datum on top of a 3D control, the 2D control becomes a 3D control.