() Stefan Monnier <monnier@IRO.UMontreal.CA>
() Sun, 15 Jan 2017 21:32:19 -0500

   How 'bout the patch below (which additionally gets you rid of
   the place where you modify a string in-place, which I find
   very untoward).

Thanks.  I have modified the mode-line munging bits to use
‘replace-regexp-in-string’ as exemplified in the patch.  OTOH,
the cursor-intangible parts of the patch i'm still mulling.

   From the bit of testing I've done, the intangibility on your
   board is a bit flimsy (C-f/C-b can move off the board), but I
   haven't tried to change that.

Yeah, it has always been partial.  At the design level, i wonder
what is the preferred user experience when about to move off the
board.  I see these possibilities:

 (a) wrap toroidally (both horiz and vert);
 (b) stay motionless;
 (c) like (b) w/ error;
 (d) do nothing special (status quo).

Personally, i don't mind (d) because i like to explore the text
properties (move point, invoke ‘describe-text-properties’), and
imagine others doing likewise.  (Too, no complaints yet.)

-- 
Thien-Thi Nguyen -----------------------------------------------
 (defun responsep (query)
   (pcase (context query)
     (`(technical mailing-list) t)
     ...))                              748E A0E8 1CB8 A748 9BFA
--------------------------------------- 6CE4 6703 2224 4C80 7502