Copyright assignment

[Venky]

I have seen a couple of post which mention stuff like "(the patch) is large enough to require a copyright assignment to be incorporated into CUPS".  Where can I find more details about this policy?  Have already searched the forums and Google.  Did not find anything much.

Would the copyright for the changes have to be assigned to Apple?  Are there any thumb rules on how bug the patch needs to be for this to apply?  And how would I go about with the assignment process?  Would the copyright be owned jointly between the contributor and Apple or would the copyright be owned solely by Apple?

Thanks, and sorry about the barrage of questions.

Cheers,
Venky.