_wp_unfiltered_html_comment

When logged in I see a hidden input as part of the comment form in the source.

<input type="hidden" name="_wp_unfiltered_html_comment" value="sOmE-nUmBeRs-HeRe" />

It is output by the do_action() function. Its seems that it enables me, as the author/admin and logged in (as I don’t see it if I’m not), to write any HTML I wish in the comments form — or at least that’s what the name suggests. I don’t see this output on my other blogs, though. But they are versions older than 2.0.10, even though they, too, have the do_action() function.

This is normal?
Was it part of the change from 2.0.9 to 2.0.10?

Thanks.