#6 Generated HTML should be XHTML compliant

[Victor Boctor]

See the following tutorial for the rules:
http://www.w3schools.com/xhtml/

The most important differences:
- XHTML elements must be properly nested
- XHTML documents must be well-formed
- Tag names must be in lowercase
- All XHTML elements must be closed

The following link can be used for validation, if the page
is hosted on the Internet. Otherwise it can be saved as
a file and uploaded to the checker.
http://validator.w3.org/check/referrer