From Xojo Documentation
Used to get and set the control’s parent control or window.
If the control is on the window, the Parent will be the Window. If the control is on the container, the Parent will be the container. If the control is completed enclosed by another control, the Parent will be that control.
If the parent control is somehow in another window, an InvalidParentException will occur.
The following example sets the parent of the control to the window.