(1) give a CSSStyleDeclaration attributes

Sure.

(2) Give an iframe a contentWindow in addition to a contentDocument

Yes but not as simple as it seems.
The linkage in decorate.c is merely a placeholder until the frame is expanded.
Look for contentDocument in http.c.
Then, I'm not sure what contentWindo means, but I suppose the window of the frame, rather than the document of the frame, check for specifications.
Even that doesn't work with your example js.

doc = ( iframe[ 0 ].contentWindow || iframe[ 0 ].contentDocument
).document

So we're grabbing window.document or document.document, the latter doesn't make any sense.

Also beware, I do some magic with content$Document which is how we expand frames automatically when their objects are referenced.
Do we need to do the same for contentWindow? Probably.
This should probably be its own patch; it's a bit more involved.

(3) Bring back the following definition for Event.

Sure I guess.

(4) Apply the Event definition from (3) to the addEventHandler

Ok.

(5) Implement childNodes.item.

Sure. Probably down in Array.prototype. Then it's part of every childNodes, and every other array, but I don't think that's a problem.
Otherwise you have to make it part of every childNodes, including those in decorate.c.

(6)

Covered by Array.prototype.item.

(7) Following on from Karl's exclusion of @ from the CSS selectors,

Yeah this is ugly but I started it, so you may as well continue it.
I do think regular expressions are more readable / intuitive, and powerful.


Karl Dahlke