Jakub Narebski [off-list ref] writes:
[*1*] From Documentation/repository-layout.txt or
http://www.kernel.org/pub/software/scm/git/docs/repository-layout.html
You can be using `objects/info/alternates` mechanism, or
`$GIT_ALTERNATE_OBJECT_DIRECTORIES` mechanism to 'borrow'
objects from other object stores. A repository with this kind
of incomplete object store is not suitable to be published for
use with dumb transports but otherwise is OK as long as
`objects/info/alternates` points at the right object stores
it borrows from.
Ah, you spotted an obsolete documentation again ;-).