gio/tests/schema-tests/override.gschema.xml

<schemalist>
  <schema id='base'>
    <key name='foo' type='s'>
      <default>'bar'</default>
    </key>

    <key name='ranged' type='i'>
      <range min='0' max='22'/>
      <default>10</default>
    </key>

    <key name='choice' type='s'>
      <choices>
        <choice value='a'/>
        <choice value='aaa'/>
        <choice value='aaaaa'/>
      </choices>
      <default>'aaaaa'</default>
    </key>
  </schema>

  <schema id='sub' extends='base'>
  </schema>

  <schema id='sub2' extends='base'>
    <override name='foo'>'baz'</override>
    <override name='ranged'>0</override>
    <override name='choice'>'aaa'</override>
  </schema>

  <schema id='sub3' extends='sub2'>
    <override name='foo'>'foo'</override>
  </schema>
</schemalist>