Internet Explorer Compatibility mode is a feature of IE that allows you to choose to render sites that targeted older versions of IE when they were developed. It essentially pretends to be IE 8 during rendering which can correct many issues. Microsoft maintains a list of sites that require this compatibility mode and allows users to choose additional sites that should be rendered using this mode. For many large enterprises that were suck on IE 6 because of the need to old legacy systems built to IE6 standards this feature proved very valuable as it enabled them to move their workstations to newer supported version of IE whilst they built replacements for their legacy systems. You can choose to enable Compatibility mode for specific sites or all intranet sites.
So what if you know that the majority of the users of your modern web application are using IE11 but with Compatibility mode on which makes their browser pretend its IE8 and thus unable to make use of new browser features? Unless you build in support for very old browsers via polyfills then those users will see errors and unexpected behaviors.
If you want to ensure that users of IE11 or Edge are not Restricted by Compatibility mode then you need to disable it for your site and this is possible by adding a meta tag to your pages. Add the below meta tag in your head tag:
<head> <meta http-equiv="x-ua-compatible" content="ie=edge" /> </head>
The page will then disable the Compatibility mode and render the page as Edge compliant modern standards. This is a very useful way to target modern browser features without having to turn off compatibility settings on each client and possibly causing issues with other sites.