X-UA-Compatible Tests

These are the values on the test pages:

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7; IE=EmulateIE9">
- IE7: behaves as expected
- IE8: renders as IE7 (expected)
- IE9(beta): renders as IE7 (not expected!)
<meta http-equiv="X-UA-Compatible" content="IE=7; IE=9">
- IE7: behaves as expected
- IE8: renders as IE8 (not expected!)
- IE9(beta): renders as IE9 (expected)
<meta http-equiv="X-UA-Compatible" content="IE=7, IE=9">
- IE7: behaves as expected
- IE8: renders as IE7 (expected!)
- IE9(beta): renders as IE9 (expected)
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7; IE=9">
- IE7: behaves as expected
- IE8: renders as IE8 (not expected!)
- IE9(beta): renders as IE9 (expected)
<meta http-equiv="X-UA-Compatible" content="IE=7; IE=EmulateIE9">
- IE7: behaves as expected
- IE8: renders as IE7 (expected!)
- IE9(beta): renders as IE7 (not expected!)
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7">
- all IEs render as IE7 (expected)
<meta http-equiv="X-UA-Compatible" content="IE=7">
- all IEs render as IE7 (expected)

My findings:

Update 2011-01-05: So Microsoft's documentation is wrong with the format. Note in the third example above that a comma was used instead of a semi-colon. This works! Thanks to the suggestion by Robocat. Stupid Microsoft who showed a semi-colon in their samples.

Despite Microsoft's own claims in their documentation and blog post, using multiple values does not always get IE8 to reliably render as IE7. Compare the tests above using IE8. Make sure you load each test in a fresh tab without fiddling with your IE8 compatibility settings or Developer Toolbar settings.

Also note: If a document has no X-UA-Compatible value but it is served in an iframe to a parent document that does: no version of IE will pass the X-UA-Compatible value to the child document. It does not inherit.

Some more links: