docs: def _listen(self, protocols, From, description):
          """
          Implementation of L{Listen}.
          """
          # The peer is coming from a client-side representation of the user
          # described by 'From', and talking *to* a server-side representation of
          # the user described by 'From'.
          self.verifyCertificateAllowed(From, From)
          theirCert = Certificate.peerFromTransport(self.transport)
          for protocolName in protocols:
              if protocolName.startswith('.'):
                  raise VerifyError(
                      "Internal protocols are for server-server use _only_: %r" %
                      protocolName)
  
              key = (From, protocolName)
              value = (self, theirCert, description)
              log.msg("%r listening for %r" % key)
              self.listeningClient.append((key, value))
              self.service.listeningClients.setdefault(key, []).append(value)
          return {}