Subsection 29.1.8 HTML Navigation
There are publisher file entries to control how navigation between pages behaves. The “Up” button may be turned on and off. An entry for the logic of these buttons can be set to the values of
linear (the default) or tree. The former causes the Previous and Next buttons to behave as if the divisions are arranged as in a printed book, i.e. linearly. The latter option means that when a reader comes to the last subdivision of a division, the Next button will be not be active, and they will need to return (up the hierarchy/tree) to the division and move to the next division. Turning off the Up button while electing the tree model is likely to lead to a frustrating navigation experience.See Subsection 44.4.16 for the exact syntax of these options.
