The Text pane, the right side of any document window tab, has 3 sub-tabs with 'Text' being the default selection. From v6.5.0, as some Tinderbox projects don’t need to export HTML at all Window menu ▸ Shown/Hide Text Pane Selector will toggle the visibility of these sub-tabs. By default, they are hidden (there is no keyboard shortcut).
When first opening the document, if the text pane selector is initially hidden, hiding it is deferred slightly to allow seeing it sliding away, helping to confirm that it is deliberately hidden (and suggesting that there is a way to recover it).
The sub-tabs are: