XHTML Rules?

http://www.ssi-developer.net/xhtml/xhtml-syntax.shtml
http://personalweb.about.com/od/basichtml/a/409xhtml.htm

1. Documents must be well-formed.
2. All element and attribute names must be lower case.
3. Non-empty elements must have a closing tag.
4. Attribute values must always be quoted
5. Attribute Minimization is not allowed.
6. Empty Elements must also be closed.
7. Whitespace in attribute values
8. The id and name attributes.