TAdvGroupBox has an AutoSize property with these sub-properties: gasBoth, gasHorizontal, gasNone, gasVertical.
Similarly, there should be a Sizable property which of course is active only when AutoSize = gasNone.
The sub-properties of Sizable should be: gsBoth, gsHorizontal, gsNone, gsVertical.
For example: When Sizable = gsVertical, then the AdvGroupBox can be sized vertically at run-time with the mouse.
This would be very useful, e.g. when one of the controls inside the AdvGroupBox has the Align property set to alClient!