Have you ever experienced IE9 crashing without prompt while visiting your newly created web site? Or even worse, your newly created website is perfectly ok; except one day your client is complaining after incidentally visiting it with IE9?
Your blood becomes cold as ice and wondered what in the heck just happened. What kind of wizard needs to de-compile the entire site in order to find what when wrong...
I have just experienced all this stuff, instantly heartlessly and rapidly!
My first response was to start testing the web page by removing whole blocks of staff, such as css or js. I was lucky enough and started removing css files. I quickly discover that a single css file was responsible for this headache. My next move was to remove half css contents (bulk remove), and again half of half content until finally after narrowing my search I end up with 10 lines of css "matter" and therefore I discovered a css property that made the whole headache:
A background property with calc() method: background-position:calc(100% - 15px) 0;
I just removed it and IE9 smiled again!
So I realized once again: don't mess with IE or your head is cut off. LOL.
Calc(): is a very nice and neat method that mathematically calculates mixed units such as pixes with percents or ems with percents, etc. This is a real powerful "code ammunition" that makes your life a lot easier. Don't use it unless you are sure you don't care for IE9 users though...