kerberos creds cache - primary principal

[Noolyg]

Hi, 

I have some questions...
I would like to know what does the "primary principal" of a ccahe
means?
I didn't really get that from the documentation...
And who is the primary principal of the default cache?
If i want to store all my creds in the default cache, but not remove
any existing ones using a different principal than the primary?
How can 2 clients use the same cache?

Thanks a lot!

:)