Writing valid HTML

If you want to check that your webpages are compliant with w3c standards visit
http://validator.w3.org/
I found quite a few errors on my new website http://www.imagemapeditor.net/

Ill list some of the things I learnt below.

• Any link tags for external stylesheets must appear in the head section of the document
• All your input tags must be ended with />
• instead of using checked to check a radio button you must use checked="checked"
• Use <br/> instead of <br>
• use onsubmit instead of onSubmit in a form