This is a good question, indeed.
Fortunately, we have prepared a Responsive Web Design sample application
that demonstrates the RadMenu behavior in RenderMode="Auto" under mobile devices.
When opened under iPad, for example, the RadMenu is rendered in the top-right corner of the screen, collapsed to a button. When touched, the menu expands. If the arrow next to an item is touched, its child items slide to view. Then, if the parent item is touched, the child items become hidden again.
If an item is clicked, the menu navigates and when the new page is loaded, the menu is rendered again collapsed as a button.
Note: Mobile rendering can be observed only under a mobile device. As this sample application demonstrates the Adaptive behavior of RadMenu, if opened in a desktop browser, the RadMenu will be rendered suitable for large screen.
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