Clone in a terminal:
# data file for the Fltk User Interface Designer (fluid)
version 1.0300 
i18n_type 1 
i18n_include <libintl.h> 
i18n_function gettext 
header_name {.hpp} 
code_name {.cpp}
decl {\#include "PopupDialog.hpp"} {public global
} 

class UserInterface {open
} {
  Function {UserInterface()} {open
  } {
    Fl_Window main_win {
      callback {Fl::delete_widget(o);} open
      private xywh {12 31 125 80} type Double selection_color 48 align 80 when 1 visible
    } {
      Fl_Button {} {
        label {click me}
        callback {PopupDialog* p = new PopupDialog(165, 55, "PopupDialog");
p->show();} selected
        xywh {25 25 70 20}
      }
    }
  }
  Function {show()} {open
  } {
    code {main_win->show();} {}
  }
} 

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