New.* and old.* as function arguments within rules

Hi,

I'm trying to make sure I understand what I'm doing.

Where is new.* and old.* documented, as regards
using them as arguments to functions called from
rules?  If it's not documented then can I rely
on this syntax continuing to work?

(It's tough searching on these strings.  :-)

TIA


Karl <kop@meme.com>
Free Software:  "You don't pay back, you pay forward."
                  -- Robert A. Heinlein