bug#60587: Patch for adding links to symbols' help documentation

[Drew Adams]

Some quick minor feedback -

1.
+  :type '(choice (const :tag "Create links" t)
+                 (const :tag "Do not link" nil))

is better as just :type 'boolean, and say in the
doc which Boolean value means which behavior.

2.
+;; Toggle on or off the linking to help documents
+(when info-make-xref-flag
+  (add-hook 'Info-selection-hook 'info-make-xrefs))

Instead of putting it on the hook when loading the
code, add/remove it in a :set function.  E.g.
(untested):

:set (lambda (sym defs)
       (custom-set-default sym defs)
       (let ((fun  (if info-make-xref-flag
                       #'add-hook
                     #'remove-hook)))
         (funcall fun 'Info-selection-hook
                      'info-make-xrefs)))

3. Maybe add a toggle command for the option, so
users can switch the behavior anytime, on the fly.

4. Or instead of having an option, maybe just have
a minor mode.

5. Face `info-color' should be named something like
`info-symbol-help-link'.

6. "clicking @kbd{mouse-2} or @kbd{mouse-1} on it"
can't be right, I think.  At least that doesn't
express what `mouse-1-follows-link' does/means.

7. Again, I think it's unhelpful to call these
links "buttons".  Especially since Info docs call
Info links "links".  That these links show their
destination in another window isn't a reason to
call them something different (and with no
definition of the additional term "button").