XML Schema: root element

The following post asks how to indicate that an element is the root element in an XML schema:

Is it possible to define a root element in an XML Document using Schema?

I have followed the w3schools tutorial on XML Schema but something is still not clear. Consider example schema 2 from https://www.w3schools.com/xml/schema_example.asp (reproduced below for convenience). How does this code indicate that <shiporder> is the root element? Isn't the example saying that all elements are valid as root elements?

------------------ instance ----------------------------------

<?xml version="1.0" encoding="ISO-8859-1"?>

<shiporder orderid="889923"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="shiporder.xsd">
  <orderperson>John Smith</orderperson>
  <shipto>
    <name>Ola Nordmann</name>
    <address>Langgt 23</address>
    <city>4000 Stavanger</city>
    <country>Norway</country>
  </shipto>
  <item>
    <title>Empire Burlesque</title>
    <note>Special Edition</note>
    <quantity>1</quantity>
    <price>10.90</price>
  </item>
  <item>
    <title>Hide your heart</title>
    <quantity>1</xample saying that all elements are valid as root elements?quantity>
    <price>9.90</price>
  </item>
</shiporder> 

----------------------- schema ------------------------

<?xml version="1.0" encoding="ISO-8859-1" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema&