At
http://www.mediawiki.org/w/index.php?title=ResourceLoader/Features&oldi…
it is written:
It starts by performing a quick sanity check that bails out if the
current browser is not supported. This saves bandwidth as well as
preventing broken interfaces, basically leaving the user with an
untouched page with the natural non-javascript fallback behavior.
Browsers such as Internet Explorer 5 and early versions of Mozilla fall
in this category.
While I see that it works, I can't find where exactly in the code is
this sanity check located. Any pointers?