<!doctype html> backward compatibility
Everything is normal in chrome and ie9 but ie8!
Firstly,I set the HTML page with HTML5 template!
Secondly,I init the iframe with an external Js document!
Then error occur in ie8 that the DOM element is undefinded,and it display while back the page to HTML4.01 template!
I have checked for HTML5 top declaration,and it is backward compatibility! So why ie8 didn't tell the page!
 
<!doctype html> backward compatibility
===

Everything is normal in chrome and ie9 but ie8!
Firstly,I set the HTML page with HTML5 template!
Secondly,I init the iframe with an external Js document!
Then error occur in ie8 that the DOM element is undefinded,and it display while back the page to HTML4.01 template!
I have checked for HTML5 top declaration,and it is backward compatibility! So why ie8 didn't tell the page!
 