If your work has to support "enterprise" clients, you'll find no shortage of companies still living in the smoldering compatibility crater where tens of thousan

If your work has to support "enterprise" clients, you'll find no shortage of companies still living in the smoldering compatibility crater where tens of thousands of old desktops met their demise. The coal-fired machines themselves have generally been retired by the forcing function of Microsoft's EOL policy for XP. So one might think this means the end of the scourge of IE8 and friends. Sadly, one would be wrong. These same large enterprises that clung to XP to wring every last drop out of those rickety HP desktops with 1.5 GB of RAM are now zealous implementers of Enterprise Managed IE. Typically there will be some old inventory system, or accounting adapter, or ERP plugin, or procurement system, that the company considers mission critical despite its decrepitude. That system itself is probably built with Microsoft's old development tools, and uses IE-flavored HTML, JScript, and ActiveX. Nobody knows how the system works anymore, its creators all died 75 years ago, and all documentation was lost in the great molasses flood. Rather than spend the time and money to rewrite these magic old black boxes, IT managers configure the entire company so that IE11 actually acts like IE8 (or, hell, sometimes even IE7), in a browser "compatibility mode", enabling their old legacy apps to run, mostly. These downgraded modes are mostly, but not exactly, like the versions they mimic. In effect, they are new, separate, subtly different browser compatibility targets for developers. IE8 itself at least has the advantage of a decade of the collective wisdom of millions applied to understanding its limitations. Ersatz IE via compatibility mode can be worse than the real thing, rife with ungoogleable issues that force developers to engage in primary research like it's the bad old days again. The kicker is that their end users all think they're "finally on IE11", and IT support often doesn't understand the subtleties of the EMIE situation. You'll hear "we're on IE11 now, so why does your app still look terrible and have strange JavaScript errors?". Allowing an exception so a specific application can run in native IE11 mode — if even possible — is often rejected as a "security risk". And why might it not even be possible? Some of these enterprises will run "vendor apps" inside a — yes — frame served by their terrible intranet system. The outer frameset document itself will be locked into downgraded compatibility mode, forcing the sites it contains to inherit that mode, and even do inexplicable and nearly undocumented things like silently replace the doctype of the framed application's pages. Or so I've heard.