fgdata/gui/dialogs/exit.xml

<?xml version="1.0"?>
<PropertyList>
  <name>exit</name>
  <modal>true</modal>
  <layout>vbox</layout>

  <text>
    <label>Exit FlightGear?</label>
  </text>
  
  <group>
    <layout>hbox</layout>
    <halign>fill</halign>
    <default-padding>10</default-padding>
    <empty><stretch>true</stretch></empty>

    <button>
      <legend>Exit</legend>
      <default>true</default>
      <equal>true</equal>
      <binding>
	<command>exit</command>
      </binding>
      <binding>
	<command>dialog-close</command>
      </binding>
    </button>

    <empty><stretch>true</stretch></empty>

    <button>
      <legend>Cancel</legend>
      <equal>true</equal>
      <binding>
	<command>dialog-close</command>
      </binding>
    </button>

    <empty><stretch>true</stretch></empty>
  </group>
  
</PropertyList>