Subject: bug#2848: describe-variable's completions vs. set-variable'scompletions

From: "Drew Adams" <[email-masked]>
Date: Wed, 1 Apr 2009 15:56:47 -0700

> default-truncate-lines is a variable defined in `C source code'.
> Its value is nil
> 
> OK, then why does set-variable not allow me to set it in the
> minibuffer? "No match".
> 
> emacs-version "22.2.1"

Because it's not a *user* variable, that is, an option.

An option is a variable that you can set using `M-x set-variable'.

Options include, as a proper subset, customizable options, that is, variables
that you can set and save using Customize.