IE9 rendering css3
===

Hi recently I have started to develop a website witch uses a few basic css3 features witch I am sure that are supported in IE9 because I've checked.No matter what I did IE9 seemed not to render any off the css3 properties not even when I was using *ms* prefix.

After I did some reasearch I found a question here on stackoverflow that dealt with a similar problem to mine and someone offered a solution to that problem.The person said to add this line in the head tag:

    <meta http-equiv="X-UA-Compatible" content="IE=9" />

After I added this everything seemed to work.What I would is an explanation as to why do I have to use this to make css3 features work in IE9 and what is it's meaning?

I am still prety new to web development and I tryed to learn html/css/javasript/php/mysql in about 6 months.While I am now capable of creating functional websites alot of gaps seemed to have been left in my head so I hope this is not a very basic question.

