Logical content order when the page is tagged: the depth-first order of the structure tree (§14.7.2), the glyphs of each content item in the order the content shows them. Content of a tagged page that is not in the tree is an artifact (§14.8.2.2.2). A page whose content holds no content item of the tree keeps page content order.
Structure = 0
ISO 32000-2 §14.8.2.5.1, §14.7.5 and §14.8.2.2.