read-multiple-choice: explain dialog popups more

* lisp/emacs-lisp/subr-x.el (read-multiple-choice): Explain
when a graphical popup is used and how it can be avoided.

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 7736225b5fa8203e3f578e5211afdce09b9a9daa..52331b9ad3657db9e59602785ea3ed19a3a61296 100644 (file)
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -214,6 +214,11 @@ user enters `recenter', `scroll-up', or `scroll-down' responses,
 perform the requested window recentering or scrolling and ask
 again.
 
+When `use-dialog-box' is t (the default), this function can pop
+up a dialog window to collect the user input. That functionality
+requires `display-popup-menus-p' to return t. Otherwise, a text
+dialog will be used.
+
 The return value is the matching entry from the CHOICES list.
 
 Usage example: