What follows are just my initial comments, on a quick read-through. Secondly there is a question of display timing in web environments, where I would prefer to be able to display the flow before the static content, rather than the other way around. Similarly other uses of top, bottom, left and right will eventually lead to user errors in multilingual setting unless deprecated. In any other case you need a separate stylesheet statement per writing direction. The presumption for page numbering seems to be that it will be based on incrementable numbering, with no overrides, or allowances for numbering using non-adjacent chararacter sequences.
Thoughts re scroll-bars and rotated viewports.
Scrollability is a feature of web tools, not printed text. Scroll bars are designed to move you from top to bottom of the viewport contents or from start to end of a line, but the convention on all computers I have seen is that the vertical scroll bar moves you from top to bottom while the horizontal one moves you from start to end. Surely either it stays as an empty tag or the end tag gets moved to the end of the text that is to go in the block. Otherwise it seems to be coming along nicely.