[turba] standard Turba attribute names, particularly '__uid'

[Otto Stolz]

Hello,

I have a working test installation with Horde 3.1.2 and Imp H3 4.1.2;
now I am trying my hans on Turba H3 2.1.3.

Currently, I am trying to get turba/config/sources.php right,
but cannot find sufficient documentation. I have checked
turba/docs/INSTALL turba/config/sources.php turba/config/attributes.php,
and the Adminstrators' FAQ.

My question is:
- Where can I find information on the standard Turba attribute names?
- In particular, what are '__key' and '__uid' (these are mapped in the
   LDAP example)?
- Will I need to map '__uid', at all, in a read-only shared address book?

I need this info to find the correct mapping to our LDAP server
for e-mail applications.

Another question:
- What is a 'freebusyUrl', and will my users find it useful?

I need this to decide what should go into each personal addressbook
(MySQL backend).

Thanks for any hint.

Best wishes,
   Otto Stolz