changes
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event is changed to ItemSelecting - tabstrip now is pageview (documentTabStrip1.TabStripElement.ItemSelecting += new EventHandler<Telerik.WinControls.UI.RadPageViewItemSelectingEventArgs>(TabStripElement_ItemSelecting))
introduce new powefull events for RadDock - SelectedTabChanging / SelectedTabChanged


Create a dock with couple of documents.
Subscribe to the TabSelecting event of RadTabStripElement and cancel it showing a message box indicating the cancellation.
The message box will be shown 5 times.