Comment 84 for bug 190848

(In reply to comment #2)
> qual="all" can actually already be used to test that a value is not set because
> it always returns true when there are no values to test. i.e. All zero values
> match.

Hmm, that sounds like a bug though. IMHO we should drop such config entirely instead of ignoring the invalid element only or warn it at least, because there may be a typo and it's hard to track down when something behaves unexpectedly.