A branch is the ordered collection of [:Revision:revision]s. for a [:WorkingTree:working tree]. Two different types of branches are planned for Bazaar-NG -- [:StandaloneBranch:standalone branches] and [:RepositoryBranch:repository branches].
In the case of standalone branches, the working tree is present for the user to work on. In the case of repository branches, the working tree is disassociated and can be represented as a [:Checkout:checkout] and merged to and from.