docs: def parameterize(self, call, host):
          """
          Parameterize a Call with its Context set to a per-host Config.
          """
          debug("Parameterizing {!r} for host {!r}".format(call, host))
          # Generate a custom ConnectionCall that knows how to yield a Connection
          # in its make_context(), specifically one to the host requested here.
          clone = call.clone(into=ConnectionCall)
          # TODO: using bag-of-attrs is mildly gross but whatever, I'll take it.
          clone.host = host
          return clone