title: XML Schema example - prefix "xs" for element "xs:element" is not bound
body: <p>The following is an example from: <a href="https://www.w3schools.com/xml/xml_schema.asp" rel="nofollow noreferrer">https://www.w3schools.com/xml/xml_schema.asp</a></p>
  
  <pre><code>&lt;xs:element name="note"&gt;
  
      &lt;xs:complexType&gt;
          &lt;xs:sequence&gt;
              &lt;xs:element name="to" type="xs:string" /&gt;
              &lt;xs:element name="from" type="xs:string" /&gt;
              &lt;xs:element name="heading" type="xs:string" /&gt;
              &lt;xs:element name="body" type="xs:string" /&gt;
          &lt;/xs:sequence&gt;
      &lt;/xs:complexType&gt;
  
  &lt;/xs:element&gt;
  </code></pre>
  
  <p>When I try validate this I get an error: </p>
  
  <blockquote>
    <p>The prefix "xs" for element "xs:element" is not bound on line 1 - XML
    Schema Problem</p>
  </blockquote>
  
  <p>What's the schema problem with this?</p>