Browse and Edit just opens the page in edit mode or a content item for editing if you have a widget on a page. The Overlay mode in 3.x is just a div that masks the background. As far as I see there is no overlay mode in 4.x editions. Is there a specific requirement for this, since there is not much functional or business logic that overlay mode brings?
Also the implementation of the page editor in 3.x is based on html div elements, since in 4.x we use RadDock controls that support drag/drop functionality.
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