How about the WebKit DOM Reference?
http://developer.apple.com/safari/library/documentation/AppleApplications/Reference/WebKitDOMRef/index.html
Update
Thanks for the comments – yes this now redirects.
Perhaps as others have said, one of the other browsers’ references would be a good place to start – then for Safari’s own DOM extensions/additions, there’s the ‘Safari DOM Additions Reference’:
https://developer.apple.com/documentation/webkitjs
Otherwise it looks like it would be a case of finding your way through the confusing set of documents there in the Safari Developer Library:
http://developer.apple.com/library/safari/navigation/