Other thoughts: 1) If I am the author to the scripts that modify document, then I am indeed aware of what gets changed. If I am not the author, I shall then not have been notified on the change. The use cases such as "debugger" do not count here - it would be possible to offer required APIs (such as DOM Mutation Events) to them only, without needing the API to populate on the page. And this is not a sucrifice to run page 50% slower caused by the Mutation Events turned on on behalf of a debugger, right?
Use cases: - user triggered input, like when using contentEditable/designMode - 3rd party libraries which want to know if the document mutates out of their context - 3rd party scripts (like ad scripts, or link to social networking or sharing sites) that change the document and the document wants to keep some sanity in it -- João Eiras Core Developer, Opera Software ASA, http://www.opera.com/
