Is it possible to provide a facility for Mutation events on e4x objects ie, something equivalent to DOMSubtreeModified in DOM Events http://developer.mozilla.org/en/docs/DOM_Events

Mutation events are a blight upon the face of the DOM. I'm fairly sure none of the browsers which implement them really like them very much; they vastly increase the relative pain of implementing functionality by introducing, to borrow the terminology of the C specification, vastly more "sequence points" where intermediate steps in execution of a method may be observed. Modifications at these points can easily disrupt improperly-maintained invariants of engine-internal code, and such cases have a disturbing tendency to result in potential security vulnerabilities, given enough tenacity, effort, and possibly luck. Beyond this, nobody hacking on SpiderMonkey really is all that fond of E4X. The spec is fundamentally broken in the way it specifies its algorithms, making it very hard to prove important properties of it. It invalidates expected JavaScript invariants and is not a good conceptual fit with the base JavaScript language. Further, even beyond just general concerns with how the specification writes its algorithms, it has been our experience that many of the bugs reported in our implementation eventually stem from specification error, even inarguable ones such as type errors, not mere semantics disagreement. I don't know anyone hacking on SpiderMonkey who is likely to be doing much beyond maintenance with the E4X implementation, and if someone not part of the community of active hackers were to submit a patch to implement mutation, I would argue strongly for not accepting it. Consequently, I'm marking this WONTFIX. E4X and DOM mutation events are both insufficiently thought out; combining the two does not fly with me, and I would be absolutely astounded if it were otherwise with any other SpiderMonkey hackers.