RadDock provides specifying a highlighting style for each docking zone using the HighlightedCssClass
property. When the dock is dragged over a zone which HighlightedCssClass
property is set if the corresponding zone is not forbidden for the dock the zone will be highlighted. You can use this for notifying users where they can drag a dock. For your convenience, I have attached a sample page which demonstrates how to achieve the mentioned above as well as a workaround for alerting a message which notifies the user if the zone over which they drag a dock is forbidden.
Please, let us know if you need further assistance.
the Telerik team