Subject: bug#19338: [PATCH 3/3] eldoc: convert `eldoc-documentation-function' into a defcustom

From: Stefan Monnier <[email-masked]>
Date: Wed, 10 Dec 2014 15:08:46 -0500

> -(defvar eldoc-documentation-function nil
> -  "Function to call to return doc string.
> +(defcustom eldoc-documentation-function nil
> +  "Function to call to return doc string for ElDoc mode.

This variable will be modified programmatically by various Elisp
packages, which interacts poorly with Custom.

If you want your describe-char-eldoc thingy to be Custom-izable, you'd
probably be better served with a describe-char-eldoc-mode minor-mode,
which you can then enable via Custom.

        Stefan