Web pages that validate to published formal grammars are well-structured documents. Well-structured documents are more easily made usable by all. Valid code is a good start in the right direction. Use the W3C Markup Validation Service to validate your code: http://validator.w3.org/.
Advanced Tip
You might want to use HTML Tidy, “a tool for checking and cleaning up HTML source files. It is especially useful for finding and correcting errors in deeply nested HTML, or for making grotesque code legible once more.” An online version of HTML Tidy is available at: http://infohound.net/tidy/.
Use a Doctype Statement
Use a doctype statement on each and every page. The doctype of the CSUN Web Template system is:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
Though the ATI calls for moving to XHTML Strict, it is a best practice at CSUN to use XHTML Transitional for now. The CSUN Web Template system is designed to be safely moved to XHTML Strict.