Reference information:
World Wide Web Consortium
They publish the standards for various mark up languages and protocols.
Here is their HTML Page: http://www.w3.org/html/
The current standard is HTML 4.01; but will soon be changing to HTML 5.0

They have an HTML Validator service, to check your pages for errors or non-conforming MU language:
http://validator.w3.org/
And other nifty tools and loads of information.

Friends don't let friends use booleans.