Read HostDockSite to access the windowed control to which the control is docked. If the control is floating, HostDockSite is a temporary control of type FloatingDockSiteClass or (if there is no floating dock site class) nil (Delphi) or NULL (C++). 

Most applications should use the ManualDock method rather than setting HostDockSite. Setting HostDockSite automatically undocks the control from its previous host (if any) and docks it to the specified control, but does not adjust the control's position and alignment and bypasses the standard docking events. 

For dock clients, the value of HostDockSite is the same as the value of Parent. For controls that are not docking clients, HostDockSite is nil (Delphi) or NULL (C++) while Parent specifies the containing control. 

DockClients 

ManualDock 

FloatingDockSiteClass 

Parent