Re: Mixed L2R and R2L paragraphs and horizontal scroll

    This means we need to allow scroll either left or right past the point
    where the first character is at the window's edge.  That is,
    window-hscroll will no longer return only zero or positive values.  Is
    that reasonable?

I think it is reasonable and necessary, once we have R2L text.  With
only L2R text, we have no need for a negative value of hscroll,
because scrolling the text away from the left window edge is useless.
With R2L text, that operation is useful because it can extend past
the left window edge.