Have a look at the property DockableSides
Friendly Name Dockable Sides
API Name DockableSides
Type Integer
Restrictions Range is 0 - 5
Get Function (dcl_Control_GetDockableSides <CONTROL>)
Set Function (dcl_Control_SetDockableSides <CONTROL> NewValue [as Integer])
Applies To Control Bar, Palette
This property determines which sides of the AutoCAD window the control bar can dock to.
Value Description
0 Left and right
1 Top only
2 Bottom only
3 Top and bottom
4 Left, right, top
5 Any side