When you’re making a website for the general public, you need to support the browsers of that general public. One of the things that can make that particularly difficult is the large install-base of older versions of Internet Explorer that don’t run in standards mode by default. Specifically, IE8 and 9 still have a combined market share of about 30 percent.
By default these versions of Internet Explorer will run in Quirks mode rather than Standards mode. This is good for websites that were made over a decade ago and targeted IE6, but it’s a disaster for modern web development because the amount of corrective CSS required is astounding. The fix is to tell them to use their edge rendering mode; that is, the closest they can get to actual standards. From there the path to proper behavior is manageable. Microsoft has explained how to do all of this in their knowledge base, but in practice it comes down to this:
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
This will instruct Internet Explorer to use a Chrome Frame if available, and if not, use the latest rendering mode available (edge). With Google having discontinued Chrome Frame though, it’s probably best to help those users to upgrade away from older Internet Explorer versions, though that’s outside the scope of this article.
So what’s the problem?
There are a few problems with the meta tag approach, the most obvious being that it doesn’t validate. It’s a Microsoft specific meta tag that isn’t part of the specification.