X-UA-Compatible: IE=9 vs IE=EmulateIE9, other browsers

Question

My company uses an application from a third party vendor, therefore we have no control over the source code. The site has compatibility issues in IE10 (only) due mostly to the rendering of Javascript, as well as in other browsers (Safari, Firefox, Chrome).

Since we DO have control over our server, I asked our Hosting team to add a custom HTTP response header in IIS as follows, based on some Googling I did.

In the Name box --> X-UA-Compatible

In the Value box --> IE=EmulateIE9

Now I'm wondering if IE=9 would've been preferable, and if that would apply to other browsers besides IE.

So my questions are, specifically:

(1) What is the difference between content=IE=9 and content=IE=EmulateIE9 ?

(2) Would using content=IE=9 force browsers other than IE to render as IE9 ?

(3) I've seen an additional attribute for Chrome=1. Does this actually work ?

The html-5.com provides this definition, so it sounds like this tag would NOT work outside of IE, but I've seen so many other references to the Chrome=1 that I'm wondering otherwise.

X-UA-Compatible is used to indicate to an IE browser which version of the rendering engine should be used to display the page. This metatag does not affect other browsers such as Firefox and Opera, which in general attempt to avoid bloating the size of the browser code by displaying web pages only one way according to established standards (Supporting multiple rendering engines presents some major challenges, especially when content rendered by one engine accesses embedded content rendered by a different engine).

Thanks!

Answer 1

1. The difference between using IE=9 and IE=EmulateIE9 is that using IE=9 forces standards mode for IE9, while EmulateIE9 will respect the DOCTYPE to determine standards or quirks mode. See this link for more details (although it's a little dated): http://blogs.msdn.com/b/askie/archive/2009/03/23/understanding-compatibility-modes-in-internet-explorer-8.aspx

See Daniel's answer for 2 and 3, but the short version is that this has zero effect on other browsers.