i just put up a ticket by mistake in the wrong sub tracker (ui).
i consider this bug as SEVER as it boils down to:
1) the jquery core selector escaping is NOT WORKING (sizzle)
2) the native selector escaping (document.querySelectorAll) DOES WORK
so the behaviour is completely ambiguous, you dont know whether to escape it or not because you never know for sure what implementation will process it (at least not in future). right now you can reconstruct the issue:
open firebug console:
jQuery("img[src*=\\\\.gif]") that will return the jquery logo image
then add a valid context that is not the document object (because document is the default context):
jQuery("img[src*=\\\\.gif]", document.body) will return NOTHING
the first line using the default context internally uses the native firefox selector function: this handles escaping correctly and according to the jquery documentation. the second line using any non-document context will run into sizzle selector implementation and that will not handle escaping as expected (or not at all?)
testing the jquery-sizzle with "img[src*=hallo\\\\]\\\\[ballo]" one can see that not only backslashes arrive as literals in the to-check-string but do not work for syntax definition either: the check string in the ATTR filter will not hold "hallo][ballo" and will not even hold "hallo\\]\\[ballo" but it will hold "hallo\\". that renders the whole escaping feature pretty useless.
but the really bad thing is, that is it ambiguous: you cannot predict what implementation will be used and therefore if you should escape it or not.