My current thinking is that the :core view in the html renderer should handle "show:folded", such that any view that uses core can then use that syntax.

When that is in place, the renderer will scan for an explicit fold.  My current thinking there is that we should use something very much like tinyMCE's page break button, only use the "fold" terminology.

If there's not an explicit fold, we'll have to take a stab at it algorithmically.