I'm afraid there's no docs on this subject, at least I've never seen such.
meantime, the quotation in my post above remains a wishful thinking, sometimes I use a cheap trick to make a caption using a 1x1 cell
while it may work for now (and it does), nevertheless it's an outdated and deprecated technic which returns us back into 1996.
basically it looks like the following snippet:
Caption text goes here
<img ... />
honestly, it doesn't worth it to bother with caption here (and now) cause it really 'would be nice to have' for WP users a control 'Use description as a caption' in the image upload section so that caption style, image border and so on all would be consistent with the theme is being used.
otherwise it may look rather randomly and distracting. the only point of captions in some of my posts is to inform a visitor they are going to open a new browser window.
PS darn, looks like they really don't want user to see the code: forum choked it down but ate all indendts I put in it to ease its readabilty.
so, once again it just proves that it doesn't worth to fiddle with any code on WP. ever.