To validate you need:
- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
-- FIRST line in file
- <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
-- FIRST html tag
- <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1" />
-- in <head> section
- Valid xhtml and CSS