PROPERTY output in Script API

Hi,

I've noticed (in the amzfs-snapshot script, anyway) that it seems
to be possible to emit a PROPERTY line on stdout from the script;
I assume that sets a property value that then gets passed to the
application run after the script?  The wiki page

http://wiki.zmanda.com/index.php/Script_API

doesn't seem to talk about that. I am curious about details,
like for how long the property stays set?  For example, if
pre-dle-estimate is run and sets a property, I assume the
application 'estimate' phase will see that property value,
and so will the script at post-dle-estimate.

Would the same property also be seen when the application is
reinvoked for command_backup?  Or does it have to be set again
by pre-dle-backup?  (I see in the case of amzfs-snapshot that
there is a pre-dle-backup that sets the property again--because
it makes a new snapshot--but I am not sure whether that would
be required for every script.)

Also it appears that scripts have the same kind of 'support'
command protocol that applications have (except they only
have to announce a smaller number of things, CONFIG, HOST,
DISK, MESSAGE-LINE, MESSAGE-XML, and EXECUTE-WHERE). That's
also not on the wiki page at the moment. Is that information
currently in flux, or is it reasonably stable? (It seems to
go back at least to 3.1.0 anyway.)

Thanks,
-Chap