Wow, Drew dug really deep into this problem and came up with some interesting stuff. Just go and read it 'cause I can't even begin to do it justice.
What can I say? I need a new thesaurus.
So .Net has some problems, along with some other tool sets, with following the rules for relative inclusions in DTDs. Drew was of course correct and I was able to create my own XmlResolver to fix the problem. BTW, the code sample in the MSDN article required some re-working for it to function properly. So now I am sure all the DTDs are loading correctly.
Upon further digging I found that there is a flat version of the XHTML 1.1 DTD that does not have the relative include problem. So I changed test.html to be:
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11-flat.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Conforming XHTML 1.1 Template</title>
</head>
<body>
</body>
</html>
Note the -flat.dtd. Now I run a very simple program using test.html:
using System.Xml;
using System;
public class _ {
public static void Main(string[] args) {
try {
XmlDocument doc = new XmlDocument();
doc.Load("test.html");
XmlNodeReader reader = new XmlNodeReader(doc);
}
catch (System.Exception e) {
Console.WriteLine(e.Message);
}
}
}
The 'x' character, hexadecimal value 0x78, cannot be included in a name.
I am a beaten man. I will drop back and punt and use XHTML 1.0 Strict, which I tested and it loads just perfectly fine, thank you.