We're told "feature detection" is much more betterer than filtering by browsers/versions... so how do you ensure support for specific versions of multiple libraries?!
I don't know what features I'm relying on directly, just what min requirements are for each library!? So when I have a constellation of libraries, what should I do to ensure the user's browser is going to support them all?
EDIT: It seems here's a partial answer, but what do you do in your production systems to warn users that their user experience may not be complete due to an old ass browser?