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diff --git a/examples/howto-flex-simple.cxx b/examples/howto-flex-simple.cxx
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+//
+// Very simple Fl_Flex demo program for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2022 by Bill Spitzak and others.
+//
+// This library is free software. Distribution and use rights are outlined in
+// the file "COPYING" which should have been included with this file.  If this
+// file is missing or damaged, see the license at:
+//
+//     https://www.fltk.org/COPYING.php
+//
+// Please see the following page on how to report bugs and issues:
+//
+//     https://www.fltk.org/bugs.php
+//
+
+#include <FL/Fl.H>
+#include <FL/Fl_Double_Window.H>
+#include <FL/Fl_Flex.H>
+#include <FL/Fl_Box.H>
+#include <FL/Fl_Button.H>
+#include <FL/fl_ask.H>
+
+// the 'Exit' button callback closes the window and terminates the program
+void exit_cb(Fl_Widget *w, void *) {
+  fl_message("The '%s' button closes the window\nand terminates the program.", w->label());
+  w->window()->hide();
+}
+
+// common callback for all other buttons
+void button_cb(Fl_Widget *w, void *) {
+  fl_message("The '%s' button does nothing.", w->label());
+}
+
+int main(int argc, char **argv) {
+  Fl_Double_Window window(410, 40, "Simple Fl_Flex Demo");
+  Fl_Flex flex(5, 5, window.w() - 10, window.h() - 10, Fl_Flex::HORIZONTAL);
+  Fl_Button b1(0, 0, 0, 0, "File");
+  Fl_Button b2(0, 0, 0, 0, "New");
+  Fl_Button b3(0, 0, 0, 0, "Save");
+  Fl_Box    bx(0, 0, 0, 0); // empty space
+  Fl_Button eb(0, 0, 0, 0, "Exit");
+
+  // assign callbacks to buttons
+  b1.callback(button_cb);
+  b2.callback(button_cb);
+  b3.callback(button_cb);
+  eb.callback(exit_cb);
+
+  // set gap between adjacent buttons and extra spacing (invisible box size)
+  flex.gap(10);
+  flex.set_size(bx, 30); // total 50: 2 * gap + 30
+
+  // end() groups
+  flex.end();
+  window.end();
+
+  // set resizable, minimal window size, show() window, and execute event loop
+  window.resizable(flex);
+  window.size_range(300, 30);
+  window.show(argc, argv);
+  return Fl::run();
+}