fgdata/gui/dialogs/save_flight.xml

<?xml version="1.0"?>

<PropertyList>
 <name>save_flight</name>
 <layout>vbox</layout>

 <group>
   <layout>hbox</layout>

   <text><label>File Name:</label></text>
   <input>
     <halign>fill</halign>
     <stretch>true</stretch>
     <property>/tmp/flight/file</property>
   </input>
 </group>

 <group>
   <layout>hbox</layout>
   <empty><stretch>true</stretch></empty>
   <button>
     <legend>OK</legend>
     <equal>true</equal>
     <default>true</default>
     <binding><command>dialog-apply</command></binding>
     <binding>
      <command>nasal</command>
      <script>
       fgcommand("save", props.globals.getNode("/tmp/flight") );
      </script>
     </binding>
     <binding><command>dialog-close</command></binding>
   </button>
   <empty><stretch>true</stretch></empty>
   <button>
     <legend>Cancel</legend>
     <equal>true</equal>
     <key>Esc</key>
     <binding><command>dialog-close</command></binding>
   </button>
   <empty><stretch>true</stretch></empty>
 </group>
</PropertyList>