* lisp/custom.el (defcustom): Mention `custom-declare-variable' in
the doc string(bug#22703).
_outside_ any bindings for these variables. (`defvar' and
`defconst' behave similarly in this respect.)
+This macro calls `custom-declare-variable'. If you want to
+programmatically alter a customizable variable (for instance, to
+write a package that extends the syntax of a variable), you can
+call that functcion directly.
+
See Info node `(elisp) Customization' in the Emacs Lisp manual
for more information."
(declare (doc-string 3) (debug (name body)))