To see what I meant, create a new buffer with "C-x b", then paste the
same text there, after setting the left fringe width to zero.
> Also, I noticed that `window-max-chars-per-line' does not take into account the variable `left-frame-width' (and
> presumably `right-frame-width').
You mean left-fringe-width, I presume? Yes, that's probably a bug.
Why is this useful, when we already have window-max-chars-per-line?
IOW, when would you like to know about the continuation glyph, and not
about how many characters can be displayed on a line?