From Xojo Documentation
Used to get and set the control’s parent control or window.
Returns Nil if the parent is the window. Assign Nil to make the control's parent the window, even if it is enclosed by another control. The child control's behavior in the IDE will reflect the parent's state. 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.