The Delete Controller button in the Track View toolbar is enabled when one or more deletable tracks are selected. This means that a plug-in can indicate to Track View that one or more of its sub-controllers can be delted via the method Control::CanDeleteSubAnim(). This provides a way for the user to delete node sub-controllers such as the visibility track, "Image Motion Blur Multiplier", "Object Motion Blur On/Off", and so on. When the user deletes a sub-animatable the method Control::DeleteSubAnim() is called.