<?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  text="Press Me" fx:id="b1" >
    <properties pp1="pp1_value" pp2="pp2_value" foo="bar"/>
  </Button>
</GridPane>