exceptions in DOM

I have sent this to www-dom@w3.org for a couple of days ago, 
but I did not really get an answer that I was satisfied with:

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What exception should be raised if you for instance call 
Comment::replaceChild or Comment::insertBefore (probably not only these).

Should my implementation raise HIERARCHY_REQUEST_ERR or NOT_FOUND_ERR?

I guess it is NOT_FOUND_ERR (?) (Since a comment can't have children)

I can't find anything about this issue in the specification...
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Perhaps the exceptions that are listed in the spec should have been 
listed in a prioritized order?

Best regards
Jan-Arve Sæther