There is not an officially documented list. It wouldn't be a bad idea to have one, but no one has done the work to gather community feedback etc.

Relatively recent Chrome, FF, Safari are obvious.

In terms of IE, 9 and 10 are definitely on the list, but I'm strongly inclined to say that IE8 should be excluded, for two reasons:

1. IE8 is missing support for most of ECMAScript 5 (e.g. modern javascript) and requires numerous polyfills, etc. to be functional. We can save ourselves a lot of coding pain by not supporting it.

2. Microsoft's mainstream support for IE8 has already ended, and extended support ends early next year. If we're writing a standardized list of browsers, I'd rather not add IE8 to that list and do work to be compatible when we're going to remove it again in a handful of months.

Currently this is just my opinion, but that's where things are at.