8.2. Looking at Gtk2::MessageDialog and interesting parts of our
program.   Gtk2::MessageDialog is a subclass of Gtk2::Dialog.
Gtk2::Dialog in turn is a subclass of Gtk2::Window.
Gtk2::MessageDialog gets created by either the new or
new_with_markup methods. The latter allows your message's text
to be formatted using Pango markup. It is quite safe to use the
latter, even if you display normal text without Pango markup,
just ensure the text string does not contain Pango markup
characters.(typically the "<" and ">" characters)   Since the
Gtk2::MessageDialog usually gets used a few times, it is good
programming practice to create a sub, or even a module where it
can be called. In the sample program, we created the sub
show_message_dialog that gets called with the type of message,
the message's text, and the buttons to display on the message as
arguments.  Importance of the parent window  To create a
Gtk2::MessageDialog, you use the following:  widget =
Gtk2::MessageDialog->new ($parent, $flags, $type, $buttons,