Re: news and docs for command-error-function

[Stefan Monnier]

> I thought it would be good to describe 3 things:
> 1. suggested way to use this variable (add-function)

All *-function variables should usually be modified via add-function, so
there's no need to include it in the docstring.

> 2. the change in its handling introduced in 24.4

Yes, it should be in NEWS, together wit the various other *-function
variables (and some fields, such as process-filter and process-sentinel)
whose default value was changed from nil to a function.

> 3. the way it could be substituted before 24.4 (a lisp snippet, like in
> http://lists.gnu.org/archive/html/emacs-devel/2013-10/msg00819.html)

This is a problem solved in 24.4 rather than introduced in 24.4, so 24.4
is not the place to document how it could have been solved earlier.

> Now I also think both the variable and the function should go to NEWS.

The function should not be documented.  It's more convenient to
have it defined as a symbol than as a lambda expression, but it should
not be called other than via the variable.


        Stefan