Document modes are deprecated
Internet Explorer 8 introduced the idea of document modes as a way to transition websites from proprietary features to features based on standards and supported by multiple browsers and devices. Starting with Internet Explorer 11, document modes are considered deprecated and should not be used. Make sure to update webpages and apps that require legacy document modes to support modern features, browsers, and devices.
Windows Internet Explorer 8 introduced document modes to help you transition from features supported by earlier versions of the browser to those specified by modern standards and other browsers. Subsequent releases of Windows Internet Explorer continued this transition by introducing new document modes that emulated features supported by earlier versions while introducing support for features defined by industry standards.
While many websites were updated to provide richer experiences based on modern features, some sites used earlier document modes in order to continue serve experiences based on older practices. In order to ensure users receive the best experience possible, earlier document modes will be phased out. Websites based on legacy techniques should be updated to rely on features defined by modern standards and practices.
Starting with IE11, edge mode is the preferred document mode; it represents the highest support for modern standards available to the browser.
Use the HTML5 document type declaration to enable edge mode:
Edge mode was introduced in Internet Explorer 8 and has been available in each subsequent release. Note that the features supported by edge mode are limited to those supported by the specific version of the browser rendering the content.
Starting with IE11, document modes are deprecated and should no longer be used, except on a temporary basis. Make sure to update sites that rely on legacy features and document modes to reflect modern standards.
If you must target a specific document mode so that your site functions while you rework it to support modern standards and features, be aware that you're using a transitional feature, one that might not be available in future versions.