[Zachery]

It appears that YUI will also need to be updated to handle the issues with the editor. Though, I don't know how reasonable that will be. I suspect we can just append similar code to the YUI file for browser matching. But I'm not overly familiar with js.

You'd want to look at

/clientscript/yui/yahoo-dom-event.js and find:

else{A=B.match(/MSIE\s([^;]*)/);

Then you'd have to append something to match Trident, instead of IE, and check for rv: instead of the MSIE version string. I'm not a pro at regex so I don't quiet understand how that regex works or what its trying to match.

I don't think any version of YUI supports IE11 though, since it was discontinued almost 3 years ago now. Before IE was even a thing.
You'd need to add something like

else{A=B.match(/Trident\s([^;]*)/);


basically, you need to patch YUI with IE11 detection. I'm not sure if the above code is correct, you'll have to dig around and check out how the user agent is parsed, and then figure out how to add the additional parsing.