Re: Mixed L2R and R2L paragraphs and horizontal scroll

     > Since R2L text lines start from the right margin, that will remain
     > true after changes in window width.  This is true independent of how
     > hscroll works.

    With L2R and R2L lines in one and the same buffer we have to decide
    which line type is given preference whenever shrinking a window
    truncates at least one L2R and at least one R2L line.  "Giving
    preference" here means which line type is allowed to place its first
    column at the respective window margin.

I think you are right, when the window shrinks that much.
However, if it shrinks but not enough to make both types truncate,
then there is no need to make a choice.