The dialogArguments IDL
attribute, on getting, must check whether its browsing context's active document's
effective script origin is the same as the dialog arguments'
origin. If it is, then the browsing context's dialog arguments must be
returned unchanged.
The returnValue IDL attribute, on
getting, must check whether its browsing context's active document's effective
script origin is the same as the current return
value origin. If it is, then the browsing context's return value must be
returned unchanged.