zeroinstall.injector.model.Feed:
An interface's feeds are other interfaces whose implementations can
also be used as implementations of this interface.
zeroinstall.support.tasks.Task:
Create a new Task when you have some long running function to run
in the background, but which needs to do work in 'chunks'.
zeroinstall.injector.trust.TrustMgr:
A TrustMgr handles the process of deciding whether to trust new
keys (contacting the key information server, prompting the user,
accepting automatically, etc)