gtk:message-dialog-format-secondary-text (dialog message &rest args)

dialog -- a gtk:message-dialog widget
message -- a Lisp format string, or nil
args -- arguments for message

Sets the secondary text for the message dialog to be message with the arguments in args. Note that setting a secondary text makes the primary text become bold, unless you have provided explicit markup. The gtk:message-dialog widget is deprecated since 4.10. Use the gtk:alert-dialog widget instead.