how to mark a portion of a TextField as readonly in javafx? (http://stackoverflow.com/questions/24864133/how-to-mark-a-portion-of-a-textfield-as-readonly-in-javafx)

Main.java

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;


public class Main extends Application{
    @Override
    public void start(Stage primaryStage) throws Exception {
        TagField tf = new TagField("find","nemo");
        Pane root = new Pane();
        root.getChildren().add(tf);
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
    public static void main(String[] args){launch(args);  }
}

TagField.java

import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.control.TextField;

public class TagField extends TextField{
    String initTag;
    String closeTag;
    public TagField(String tag,String text){
        this.initTag = "<" + tag + ">";
        this.closeTag = "</" + tag + ">";
        setTagText(initTag + text + closeTag);
        super.textProperty().addListener(new ChangeListener<String>(){
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                if(!newValue.contains(initTag)||!newValue.contains(closeTag)){
                    setTagText(oldValue);
                }
            }
        });
    }
    public void setTagText(String text){
        super.setText(text);
    }
}