ant/src/etc/testcases/taskdefs/optional/script_reference.xml

<project name="test-reference" default="script">
  <target name="script">
    <script language="javascript">
    </script>
  </target>
  <target name="def">
    <taskdef name="my.echo" classname="org.apache.tools.ant.taskdefs.Echo"/>
    <my.echo id="my.echo.ref" message="hello world"/>
  </target>
</project>