<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<GridPane xmlns:fx="http://javafx.com/fxml">
  <Button onAction= <error descr="No controller specified for top level element">"#foo"</error> text="foo" fx:id="b1" />
</GridPane>