RE: Using "Emacs Configure" **and** modifying .emacs

[Drew Adams]

> > It is fine to use Lisp. It is generally not
> > advisable to use it without knowing what the
> > functions you use do (or don't do).
> > That's one way to learn, of course, - by
> > experimenting, but it can also help to read
> > the fine manual.
> 
> For setting single variables, one would think
> using common sense, and the kind of common
> sense that comes with using computers every day
> and evermore pushing the envelope to increase
> one's understanding, it would seem this would
> be enough, at the very least if the docstring
> (help system) also is consulted for the
> specific setting. But reading the manual is
> always encouraged, of course.
> 
> If the docstring isn't enough, but the manual
> is, one can report it as a bug and suggest how
> the docstring can be improved.

Yes, the doc string for such an option should warn you
not to just use `setq'.  But not every doc string is
perfect. ;-)

The Elisp manual, node `Variable Definitions' says:

‘:set SETFUNCTION’
     Specify SETFUNCTION as the way to change the value of this option
     when using the Customize interface.  The function SETFUNCTION
     should take two arguments, a symbol (the option name) and the new
     value, and should do whatever is necessary to update the value
     properly for this option (which may not mean simply setting the
     option as a Lisp variable); preferably, though, it should not
     modify its value argument destructively.  The default for
     SETFUNCTION is ‘set-default’.

     If you specify this keyword, the variable’s documentation string
     should describe how to do the same job in hand-written Lisp code.
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

http://www.gnu.org/software/emacs/manual/html_node/elisp/Variable-Definitions.html

Note the second paragraph.  If you define an option with a
`defcustom' that uses `:set', help users of your option by
letting them know how to change the value using Lisp.  How
to change the value typically does not mean using only `setq'
in such a case.