I'm doing a detailed exploration of all the information returned by FN
GETCATINFO, and now I'm into the really obscure stuff.  among the
"extended Finder info" that GETCATINFO returns for folders
(ioDrFndrInfo), there's a sub-field called "frOpenChain," which I'm
trying to figure out.  Inside Mac describes it only as a "directory ID
chain of open folders."  I thought it might have something to do with
the chain of little "triangle toggles" in the directory's Finder window,
but I can't find any pattern to the results. 90% of the time, I get the
value $C3400000, and the other 10% of the time, the value $00000000. 
Never anything else.  Doesn't seem to matter what folder I choose, nor
what folders are open on the Desktop, nor anything else I can think of.

Anybody have a clue?

Thanks.
 - Rick