On Mar 9, 2020, at 1:20 PM, Eli Zaretskii <eliz@gnu.org> wrote:

From: Yuan Fu <casouri@gmail.com>
Date: Mon, 9 Mar 2020 11:44:51 -0400
Cc: eliz@gnu.org,
emacs-devel@gnu.org

Without truly filling the lines, do the commands C-a, C-n, etc work properly?

It depends on the commands: C-n/p works fine (given
line-move-visual is t), but C-a/e moves to the end of buffer line,
which is the beginning/end of the paragraph in a users eyes

I was afraid it would be like that.

I suppose that the rectangle commands don't work, and C-x = does
something unhelpful.  Is that so?  What about C-x TAB?

If all the commands that ought to make sense for such text
understand how the display shows the line-wrapping, and DTRT,
I suppose that will be as good as real wrapping.  Would you like to
work on that?

For all the commands, the behavior of flywrap (I’m calling it flywrap now) should be identical to that of normally redisplay word wrapping:

No, with word-wrap C-a/C-e work as you'd expect: they move to the
beginning/end of the visual line, not the physical line.