typedef void __fastcall (__closure *TGetSiteInfoEvent)(System::TObject* Sender, TControl* DockClient, System::Types::TRect &InfluenceRect, const System::Types::TPoint &MousePos, bool &CanDock);
Sender is the dock site.
DockClient is the control being dragged.
InfluenceRect is the rectangle in which the mouse must be positioned for the dock site to accept a dragged control. By default, InfluenceRect is the area of the target control, expanded by 10 pixels on each side. This can be adjusted by the event handler.
MousePos is the position of the mouse pointer.
CanDock returns whether the dragged control can be docked to the dock site.