The RibbonbarMenu and RibbonBarSplitButton are only container controls and do not support the CommandName property, as they don't trigger any command when clicked - they only open their dropdown to visualize the available child items. The CommandName and CommandArgument properties are supported by their respective children - RibbonBarMenuItem and RibbonBarButton. A small exception can be made for the SplitButton, which can trigger a command when pressed in the button area. However all this does is execute the command of its first child button.
You can easily check the available properties of each item in VisualStudio via Intellisense, as shown in the attached image.
All the best,
Bozhidar
the Telerik team
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