To achieve what you need you could use the IsSelected property of the RadPane control (which is inherited from the RadTabItem) and which value is true when the pane is currently the visible pane in its group. It is the same for the unpinned panes, which are placed in the AutoHide area. Alternatively you could use the SelectedItem property of the RadPaneGroup or AutoHideArea (which is inherited from the RadTabControl) which holds a reference to the currently visible pane in the corresponding group.
Hope this helps.
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the Telerik team
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