> So if the entire buffer uses just a single font, like TUTORIAL.he
> does, you do the test only once, at the first character of the buffer
> text?  But that could produce incorrect results, because the text
> further into the buffer could have both RTL and LTR paragraphs
> intermixed, and the correct display will show each of these at their
> correct base direction.  For example, most of the paragraphs in
> TUTORIAL.he have right-to-left base direction, but the last paragraph,
> with the Local Variables, is left-to-right, so its display starts at
> the left edge of the window.
>
Intermixed paragraphs are fine though mixed text is slightly problematic
(see attachment).

The window positioning information can only be obtained for the part
> of the buffer text actually visible in a window; for buffer positions
> outside of the viewport posn-at-point will give you nil.  How do you
> work around this limitation to allow printing text of the entire
> buffer?

You are correct with your doubts. And unfortunately, I don't have all the
answers. That's why in all my communication I've always maintained "Basic"
WYSIWYG. Maybe somebody else can improve upon the algorithm.