plugins/javaFX/testData/highlighting/acceptReferenceInsideDefine.fxml

<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<GridPane xmlns:fx="http://javafx.com/fxml">
    <Button fx:id="btn1"/>
    <fx:define>
        <fx:reference source="btn1"/>
    </fx:define>
</GridPane>