Re: Mixed L2R and R2L paragraphs and horizontal scroll

 >> Because it's no more a window but a line property, IIUC.  When, after
 >> scrolling the first line, you move `point' to show another portion of
 >> the second line like this
 >>
 >>        +---------+---------+-------------------+
 >>        |$ijk     |abcdefgh$|abcdefghijk        |
 >>        |KJIHGFED$|$HGFEDCBA|        KJIHGFEDCBA|
 >>        |         |         |                   |
 >>        +---------+---------+-------------------+
 >>
 >> you get two different non-zero values of `window-hscroll'.
 >
 > No, you don't necessarily get two different values.  The value from
 > the second line defines a scroll from the right margin, not from the
 > left.  (Which probably means it's not a good idea to have
 > window-hscroll return a negative value in that case.)

When you hscroll the second line we must be able to return that somehow
- otherwise how would we know?  So either we have to invent a new
function like `window-RL-hscroll' or interpret the return value of
`window-hscroll' appropriately.  And this function must probably handle
lines containing both LR and RL text correctly.

 >>  >       +---------+---------+-------------------+
 >>  >       |$ijk     |abcdefgh$|abcdefghijk        |
 >>  >       |     KJI$|$HGFEDCBA|        KJIHGFEDCBA|
 >>  >       |         |         |                   |
 >>  >       +---------+---------+-------------------+
 >>  >
 >>  > Is this what you are suggesting?
 >>
 >> This would be needlessly inconvenient.
 >
 > Why inconvenient?

Inconvenient for the user.  Why scroll something out of view if there's
no urgent need to do so.  (Although a similar argument could be made for
pure LR text as well - why scroll the entire window when I want to see
the last characters of the single overlong line in my entire text.  With
automatic line-wrapping turned off, I mean.)

 > That's what would happen if the second line was
 > displayed at the left margin, like this:
 >
 >       +---------+---------+-------------------+
 >       |$ijk     |abcdefgh$|abcdefghijk        |
 >       |$IJK     |$HGFEDCBA|        KJIHGFEDCBA|
          ^^^^^^^^^
 >       |         |         |                   |
 >       +---------+---------+-------------------+

I fail to understand the marked text in your example.

 > The advantage is that all the lines scroll in lockstep, albeit in two
 > different directions, and `window-hscroll' can still return a single
 > value whose meaning is well defined.

So it would be convenient for the designer.

 >> Hence, `window-hscroll' should probably return the value for the
 >> line `window-point' is on.
 >
 > That's also possible.  Are the users of this function normally
 > interested only in the amount of scroll of the current line?

Mostly for calculating the argument of `set-window-hscroll' I suppose.
But I have never looked into this.

martin