Will IE11 support compatibility modes once support for leagcy browsers is dropped?

Question

With the support for legacy Internet Explorer browsers being dropped on January 12th, I'm left wondering what Microsoft plans to do with the rendering engines that support the "compatibility" modes for previous versions of the browser... will support for them be more gradually phased out? or will they be as vulnerable as the full browsers?

For anyone somehow not familiar, a webpage can claim compatibility with a legacy version of Internet Explorer (and thus indicate dependence upon features that have in large part been phased out by or at least cloaked in newer versions of Internet Explorer and it's successor, Edge) by using a <meta http-equiv="X-UA-Compatible"...> tag and specifying your preferred compatibility. Microsoft has stated that essentially Spartan/Edge "will only honor custom docmodes for intranet sites, sites on Enterprise CV list, and when in EMIE" -- but that was a year before support for the browsers was to be dropped. I wonder what that means for IE11 going forward... anyone know? If they will do so at the beginning, how long will they, for instance, support IE5 compatibility? or IE7?

Answer 1

Microsoft's support focuses on the browser (e.g. the .EXE) not its features, (e.g. document compatibility or their respective rendering "engines"). Thus, IE11 remains in support and will, presumably, continue to receive updates the company deems appropriate--potentially including fixes to document mode rendering.

As far as support for document modes (the various rendering engines you refer to) goes, they were formally deprecated in IE10 and made obsolete with the release of IE11 RTM.

These words have specific meaning in Microsoft documentation. The former means the feature might work moving forward, but there's no guarantee. The latter means it's highly likely the feature will not work moving forward and it's time for you to use another.

This suggests that it's highly unlikely that any further updates to document modes will be issued for IE10 or earlier. There may be fixes released for IE11, but that will only remain true as long as IE11 remains in support.

Edge doesn't support document modes. (Indeed, the twitter feed of a certain IE Dev team member frequently report, with glee, the thousands of lines of document mode-related code ripped out of the code base.)

In brief, document modes (and their respective rendering engines) are a thing of the past and should be treated accordingly.

One caveat should be made: It's possible that IE11 might be updated to fix problems in document modes that it supports. As long as IE11 remains in support, that's a possibility.

And, truth be told, there's a small possibility that an update might be issued for earlier versions of IE (as was done for IE6 shortly after support ended for XP), however, the bar for that would be tremendously high and it certainly wouldn't happen very often.