Three more quirks-mode-triggering doctypes were just added to HTML 5 (see <http://html5.org/tools/web-apps-tracker?from=1301&to=1302>). We should make sure these trigger quirks mode in WebKit.
These doctypes are already listed and triggers quirks mode in DocTypesString.gperf: "-//o'reilly and associates//dtd html extended relaxed 1.0//en", PubIDInfo::eQuirks3, PubIDInfo::eQuirks3 "-//softquad software//dtd hotmetal pro 6.0::19990601::extensions to html 4.0//en", PubIDInfo::eQuirks, PubIDInfo::eQuirks "-//softquad//dtd hotmetal pro 4.0::19971010::extensions to html 4.0//en", PubIDInfo::eQuirks, PubIDInfo::eQuirks So the bug report is in my opinion irrelevant.
Closing as WORKSFORME as we already support and more importantly test these doctypes.