<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.layout.*?>
<?import javafx.scene.image.*?>

<AnchorPane xmlns:fx="http://javafx.com/fxml" fx:controller="MyController">
  <fx:define>
    <fx:include fx:id="foo" source="btn.fxml"/>
  </fx:define>
</AnchorPane>