Beginner question

[Gatorajc]

I am learing XML out of a book and have been going through the examples. Well the following example says it should throw error indicating that it is not valid. But guess what it does not. It runs fine. Is it because the way I am opening the file in the browser or what.

<?xml version = &quot;1.0&quot;?>
<!DOCTYPE note [
<!ELEMENT note ( message )>
<!ELEMENT message ( #PCDATA )>
<!ATTLIST message
number CDATA #REQUIRED
date CDATA #REQUIRED
from CDATA #FIXED &quot;Kathy Shepherd&quot;>
]>
<note>
<message number=&quot;10&quot; date=&quot;073001&quot; from=&quot;someone else&quot;>
Remember to buy milk on the way home from work
</message>
</note>

Any help to this XML beginer I would be very grateful. AJ
I would lose my head if it wasn't attached.