Re: Mixed L2R and R2L paragraphs and horizontal scroll

[Richard Stallman]

    > Maybe there SHOULD be a specified line length for this purpose.
    > (Perhaps fill-column?  Or "use fill-column" could be one of the
    > settings.)  nil could mean "use the window width".
    > 
    > When the width is specified, not nil, then the right behavior
    > is to use that width even if it causes truncation.

    You are talking about introducing a new feature.  That could be good,
    but for now I'd like to have a bidi display without new features.

Ok, let's stick to the case where the window width controls it.

    > Horizontal scrolling should apply to the whole window contents
    > in a rigid fashion.

    But that cannot be done in this case, because the second line cannot
    be scrolled to the left without moving its first character A from the
    right margin.

Horizontal scrolling does whatever we make it do.  The question
is what behavior is best.

I'm saying that horizontal scrolling should move the window contents
rigidly left or right, just as vertical scrolling moves the contents
rigidly up or down.

Perhaps with bidi text we should allow negative hscroll, in other
words, scrolling the whole contents to the left of the usual position.

The definition of hscroll is not the same as how we number columns for
indentation purposes.  Indentation is defined in terms of the order of
text in the buffer.  In a line that is entirely RTL, indentation needs
to start from the right margin and work leftward.  By contrast,
horizontal scrolling is defined in terms of left and right, not
forward and back.