What does <meta http-equiv=“X-UA-Compatible” content=“IE=edge”> do?

Question

What\'s the difference if one web page starts with

Answer 1

I think this diagram from Microsoft explains all. In order to tell IE how to render the content, !DOCTYPE has to work with X-UA-Compatible meta tag. !DOCTYPE by itself has no affect on changing IE Document Mode.

http://ie.microsoft.com/testdrive/ieblog/2010/Mar/02_HowIE8DeterminesDocumentMode_3.png