Re: Mixed L2R and R2L paragraphs and horizontal scroll

    That can be done, but then we will probably need to introduce some new
    display features to indicate that the first character is scrolled off
    the margin.

The margin glyphs indicate that; I don't we need to change anything there.

    > The definition of hscroll is not the same as how we number columns for
    > indentation purposes.

    That's true, but the effect of hscroll is defined in terms of columns,
    so I think it's best not to break the relation between column
    numbering and hscroll.

The relation is that they count in the same units.  R2L text will not
alter that relationship in any case; one column as regards scrolling
will still be one column as regards indentation.