Re: Mixed L2R and R2L paragraphs and horizontal scroll

[Richard Stallman]

    Let me start with an example of 2 single-line paragraphs (the frame
    around the text shows the window borders):

          +---------------------------------------+
          |abcdefghijk                            |
          |                            KJIHGFEDCBA|
          |                                       |
          +---------------------------------------+

Why are there 28 spaces; what makes KJIHGFEDCBA end at column 39?
Is that determined by the width of the window, or by some separate
setting analogous to fill-column?

    Looks okay, right?  But what if I split the window horizontally (with
    "C-x 3"):

          +-------------------+-------------------+
          |abcdefghijk        |abcdefghijk        |
          |        KJIHGFEDCBA|        KJIHGFEDCBA|
          |                   |                   |
          +-------------------+-------------------+

    Does this look correct?  Is anyone bothered by the fact that the
    relative horizontal position of the two lines has changed, and yet
    there are no line truncation glyphs anywhere in sight?

I think users will be happy with it.  If the column where KJIHGFEDCBA
ends is determined by the width, then this is the behavior that follows
the rule.  Anything else would be inconsistent.

      But Emacs does not
    have a rigid line length, so flushing the R2L lines against the right
    margin of the window makes their position depend on the window width.
    Is that okay?  (I think it is.)

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.

    Now the crucial question: what do you think should happen if I scroll
    the leftmost window horizontally so that the end of the first line
    (the characters "ijk") become visible?  I think it should be this:

          +---------+---------+-------------------+
          |$ijk     |abcdefgh$|abcdefghijk        |
          |$HGFEDCBA|$HGFEDCBA|        KJIHGFEDCBA|
          |         |         |                   |
          +---------+---------+-------------------+

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