Fx:include and fx:script - when is the included fxml file parsed?

Question

I'm curious to know when an included (via fx:include tag) fxml document is parsed and if a script defined in the main fxml document can reference elements from the included document. The example below results in the following error message: +"sun.org.mozilla.javascript.internal.EcmaError: ReferenceError: "loadOrdersButton" is not defined. (<Unknown source>#2) in <Unknown source> at line number 2"+
Example:
Main.fxml
The script fails to find the loadOrdersButton defined in HeaderFields.fxml. (Yes the button's fx:id is set to loadOrdersButton)
<?xml version="1.0" encoding="UTF-8"?>
<BorderPane prefHeight="800.0" prefWidth="1200.0" xmlns:fx="http://javafx.com/fxml">
    <top>
            <fx:include source="HeaderFields.fxml">
                <fx:script><![CDATA[
                    loadOrdersButton.setVisible( false );
                ]]></fx:script>
            </fx:include>
    </top>
    <center>
    </center>
</BorderPane>
HeaderFields.fxml
<?xml version="1.0" encoding="UTF-8"?>
<AnchorPane xmlns:fx="http://javafx.com/fxml">
  <children>
    <Pane>
      <children>
        <Button fx:id="loadOrdersButton" />
      </children>
    </Pane>
  </children>
</AnchorPane>

Answer 1

I'm curious to know when an included (via fx:include tag) fxml document is parsed It is parsed as soon as it is encountered. In other words, the include is fully processed before the next element in the including file is processed.
and if a script defined in the main fxml document can reference elements from the included document.It cannot. FXML IDs are considered "private" to the document and its associated controller (or any script code directly defined or referenced by that document). It is not possible to "inject" script code into an include as you appear to be attempting to do here.
However, an include's controller is accessible to the including document. So if the controller for HeaderFields.fxml exposed a "loadOrdersButton" property via a getLoadOrdersButton() method, you could do something like this:
<fx:include fx:id="headerFields" source="HeaderFields.fxml"/>
<fx:script><![CDATA[
    headerFieldsController.loadOrdersButton.setVisible(false);
]]></fx:script>Of course, another option is to simply include the script in the HeaderFields.fxml file itself:
<Button fx:id="loadOrdersButton" />
<fx:script><![CDATA[
    loadOrdersButton.setVisible(false);
]]></fx:script>But I'm assuming there's some reason you don't want to do that.