## The problem
Customize throws an error when trying to set characters in the Whitespace Mode display mappings. When I paste the symbols I want into the Customize fields, it says "This field should contain a single character." Even though I've only deleted and entered a single character! There's a lot more documentation about the syntax of setting the variable in code than through the Customize interface, so I'm not sure if Customize is broken or if I'm misunderstanding something. But when trying to edit more than one display mapping, this error is at least vague and unhelpful.
## My system setup
* Fedora 26 Workstation x86_64
* Emacs 25.2.1 in an X window, with GTK+ 3.22.16
* Whitespace Mode 13.2.2 (packaged with Emacs, in Fedora)
## Steps to reproduce
1. Launch Emacs without any other configuration (`emacs --quick`).
2. Execute Customize and search for Whitespace Display Mappings.
3. Edit the character mapping. For example, delete the default "$" used for newlines, and paste "↵" (U+21b5 "Downwards Arrow With Corner Leftward").
4. Click Apply. See the error in the mode line at the bottom of Emacs
I thought at first that Customize wasn't accepting Unicode characters that might be more than a single byte, but I actually tried resetting all mappings to default, then editing the newline mapping to replace the default "$" with another ASCII character, "&", and it *still* says "This field should contain a single character."
I ended up setting the display mapping manually from my config file.
(setq whitespace-display-mappings '(
;; Plain space: · or .
(space-mark 32 [183] [46] )
;; Non-breaking "hard" space: • or _
(space-mark 160 [8226] [95] )
;; Newline: ↵ or ¬ or $
(newline-mark 10 [8629 10] [172 10] [36 10])
;; Tab: ⇥ or » or \
(tab-mark 9 [8677 9] [187 9] [92 9] )))
*This* works as expected.
But I can't figure out why I couldn't do this in Customize. What do you think?
Thank,
~ Andrew