Re: doc elisp intro cross reference fixes

[Luc Teirlinck]

Stefan Monnier wrote:

   Could someone explain to me the subtle differences between:
   - defvar with a * in the docstring.

Customizable through `set-variable', but not through Custom.

   - defcustom with no * in the docstring.

Customizable through Custom, not with `set-variable'.  Usually
necessary if setting the variable directly has no effect.

   - defcustom with a * in the docstring.

Customizable through both.

Of the three the one that is not obviously useful is the first.  But
there are (infrequent) situations where it might seem reasonable.

Sincerely,

Luc.