Is the xml validator at w3schools ok?

Hi all,

While just checked http://www.w3schools.com/xml/xml_validator.asp, there is an xml validator, which alerts "No errors found" for the given xml, <?xml version="1.0" ?>
<!DOCTYPE note [
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<message>Don't forget me this weekend!</message>
</note>
Is that OK?
(I'm just learning the basics of xml :o)