Render page in IE8 like IE9

I'm trying to get my website to specify the document compatibility mode using:

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE9">

I want to be able to use CSS3 such as border-radius however, it doesn't work in IE8. I thought this is what开发者_开发百科 X-UA-Compatible is supposed to do, render the page as if the visitor was using IE9.

What am I missing?

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IE9 can render pages like IE8, because IE9 is newer, it knows how to do it.

The contrary is impossible. IE8 is way older than IE9, so he has absolutely no ideas on how to render HTML5 and CSS3.

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IE8 isn't going to 'know' IE9, since IE9 comes after. While I'm not familiar with the tag, I'm willing to bet it's designed to allow backwards compatibility.

Trying to use it to induce forwards compatibility is nonsense. IE8 doesn't know how to do CSS3 and other fun stuff, and telling it you want it to act like IE9 doesn't change that.

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You can try CSS PIE.