Udacity Android Courses use RelativeLayout not ConstraintLayout

https://classroom.udacity.com/courses/ud834/lessons/4034888704/concepts/5b798321-219a-4910-9be1-7fcac1e5b8dc

The following XML is for the course:

https://classroom.udacity.com/courses/ud836

and it runs fine on my Nexus 5 phone.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.android.justjava.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
</RelativeLayout>