Invisible or semi-invisible posts :)

I mentioned this in an unrelated thread but several responses down so doubt any/many saw it.

Don't know if this is practical or desirable, but what if there was a way to mark a post as invisible.

What do I mean by that you ask?

What if I could reply to a post and mark it as invisible. An e-mail notification with my response would go out to anyone that is watching the topic, but would not result in a visible post to the forum.

Might be useful for something where I just wanted to seek a clarification about someone else's response, suggest a change/correction to their response. Sometimes I make a mistake (don't mean a typo, but bad/incomplete answer - rare but does happen, or maybe I just misinterpreted the original question)) and this way someone could let me know to clarify/correct/expand my earlier response with out having to add more posts to the thread.

Maybe instead of calling this an invisible post, maybe it should be considered a "Notify Topic Watchers".

Anyone else think of a way to use something like this?

One problem might be that some folks would mark something invisible that really should be part of the visible thread. Now what do you do?