It turns out to be fascinating as to what you can and cannot do.
@GaryP - you can always add a second line with the Text Tool directly to the "simple text", even when the NavBar is fully grouped.
What you cannot do is add it through the Edit NavBar window, which ignores line feeds.
@delver - you have found a weakness in Xara'a approach to text boxes, which are no use here as only "simple text" is allowed.
I will raised this as a general text feature request. It probably will not not percolate through to NavBars through.
I build my own NavBars from Buttons and Layers - much more control - images, different rollover effects, different styles of menus.
I also prefer using CSS NavBars over Xara' solution as an alternative.
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