The value is determined automatically, based on the type of the end-user's device: touch or non-touch. Corresponds to Ribbon under non-touch device browsers. Corresponds to OneLineRibbon under touch device browsers.
An external ribbon is used by the Spreadsheet as a toolbar.
The Spreadsheet has no toolbars.
The built-in ribbon displays all items in an active tab on one line.
The toolbar for the Spreadsheet is rendered as a built-in ribbon.