No decision control once FO is produced. Fire and forget processing. They have formatting features requiring layout decisions. Preform at tables in three widths on long pages, compare area trees, use width with least area and no overflow. There’s no standard XML format for area tree. SVG? For graphics, image magical identify for size and resolution.
XSL-FO charter has run out. There’s a FOP extension for working with AreaTree. Use Saxon-CE event model for XSL-FO? I encouraged him to create an extension for working with AntennaHouse AreaTrees.