This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
In particular, explicitly passing "undefined" for the first argument is treated as "false" in implementations, but as "true" in CSSOM View as currently specced. See similar issues in other APIS at https://www.w3.org/Bugs/Public/show_bug.cgi?id=23565 and https://www.w3.org/Bugs/Public/show_bug.cgi?id=23564
https://dvcs.w3.org/hg/csswg/rev/f0140b0673ff