"... the window start at a meaningless point within a line."

[Alan Mackenzie <acm@muc.de>]

Hello, Emacs.

In the Elisp manual, page "Window Start and End", it's described how, if
in (set-window-start x) x is a position not at the start of a line, the
display engine will, instead of x, choose some value near x as the
window start.  Is this really necessary?  It causes problems.

The particular problem I'm looking at is with Follow Mode, where a pair
of adjacent windows are of unequal width.  This is a very common
scenario - I frequently use Follow Mode with three side by side windows
of widths 79, 79, and 80 (as measured by window-body-width).

The problem occurs when there's a long line at the bottom of window 2
and its continuation line at the top of window 3.  The display manager
chops off the line in W2 after 78 characters, and inserts a \ sign.  It
then starts the continuation line in W3 at character 80 (counting from
1), assuming as it does, that the previous line in this window would be
79 characters long.  So character 79 appears neither on the first
portion of the line in W2, nor in its continuation in W3.  This is
suboptimal.

This problem would not occur if there were a flag to set-window-start
meaning "this value really is where I want the window to start, not some
beginning of line nearby".

How difficult would it be to relax the constraint on window start
positions and implement this flag?

-- 
Alan Mackenzie (Nuremberg, Germany).