Documentation not clear for the Lisp function set-variable

[Yoni Rabkin]

Hello, I'm on CVS GNU Emacs 22.0.50.1

As far as I understand, the function set-variable, called
interactively will only tab-complete the names of variables defined as
"interactive".

This fact is not stated in the documentation string for set-variable.
This is only mentioned (or could be understood) from the documentation
itself. The documentation string reads as follows:

"Set VARIABLE to VALUE.  VALUE is a Lisp object.
When using this interactively, enter a Lisp object for VALUE.
If you want VALUE to be a string, you must surround it with doublequotes.
VALUE is used literally, not evaluated.

If VARIABLE has a `variable-interactive' property, that is used as if
it were the arg to `interactive' (which see) to interactively read VALUE.

If VARIABLE has been defined with `defcustom', then the type information
in the definition is used to check that VALUE is valid.

With a prefix argument, set VARIABLE to VALUE buffer-locally."

This caused the following confusion: A user logged onto the #emacs irc
channel and asked why the variable frame-title-format was not listed
in the tab-completion for M-x set-variable.

This means that we have at least one case of someone being confused be
this. Since the name of the function is "set-variable", the limited
scope is not immediately clear.
-- 
"Cut your own wood and it will warm you twice"
        Regards, Yoni Rabkin Katzenell