Lisp manual is incomplete w.r.t. mode-line-format

[Kevin Rodgers]

In GNU Emacs 21.3.2 (i386-pc-solaris2.8, X toolkit) of 2003-05-22 on
zeus, the documentation for mode-line-format (in the Emacs Lisp
Reference Manual edition 2.8) is incomplete.

In describing a symbol or a list whose car is a symbol, the doc string
says the symbol's value is used, from which I would infer that the
symbol must be bound.

But the Lisp manual says that a SYMBOL construct whose value is void is
ignored.  That's OK, as that level of detail may not be appropriate for
the doc string.

But the manual does not say anything about an unbound symbol in a
(SYMBOL THEN [ELSE]) construct.  Experiment shows that when SYMBOL is
void the ELSE element is used, rather than ignoring the entire
construct.  Is that the correct behavior?  It should be documented.

The manual also says that "A list whose first element is a symbol that
is not a keyword specifies a conditional".  So how should (:KEYWORD ...)
be interpreted?  Experiment shows that (:foo "bar") is "bar", but (:foo)
is "*invalid*".

Finally, the manual does not explain what the result is when (:eval
FORM) causes an error.  From experiment, it is ignored.

Thanks,
--
Kevin Rodgers