I switched from trunk to branches/safari-601.1-branch, and my build fails. What happened was that CSS_SELECTORS_LEVEL4 got disabled, but these derived files didn't get rebuilt. SelectorPseudoClassAndCompatibilityElementMap.gperf SelectorPseudoElementTypeMap.cpp SelectorPseudoElementTypeMap.gperf FWIW, this is the complete list of old derived files in WebCore, not sure if the others being old also means bad things. ColorData.cpp EventFactory.cpp EventHeaders.h EventInterfaces.h EventTargetHeaders.h EventTargetInterfaces.h ExceptionCodeDescription.cpp ExceptionCodeDescription.h ExceptionHeaders.h ExceptionInterfaces.h HTTPHeaderNames.cpp HTTPHeaderNames.gperf HTTPHeaderNames.h SelectorPseudoClassAndCompatibilityElementMap.cpp SelectorPseudoClassAndCompatibilityElementMap.gperf SelectorPseudoElementTypeMap.cpp SelectorPseudoElementTypeMap.gperf JSWebKitMouseForceEvent.cpp JSWebKitMouseForceEvent.h JSVideoStreamTrack.cpp JSVideoStreamTrack.h JSAudioStreamTrack.cpp JSAudioStreamTrack.h DOMWebKitMouseForceEvent.h DOMWebKitMouseForceEvent.mm DOMWebKitMouseForceEventInternal.h DOMVideoStreamTrack.h DOMVideoStreamTrack.mm DOMVideoStreamTrackInternal.h DOMAudioStreamTrack.h DOMAudioStreamTrack.mm DOMAudioStreamTrackInternal.h WebReplayInputs.cpp WebReplayInputs.h CharsetData.cpp HTMLEntityTable.cpp UserAgentScripts.h UserAgentScriptsData.cpp XMLViewerCSS.h XMLViewerJS.h XPathGrammar.cpp XPathGrammar.h DedicatedWorkerGlobalScopeConstructors.idl WorkerGlobalScopeConstructors.idl