code: def add_peer_address(self, ext_bgp_peer_or_fw, rank=None):
          
          if ext_bgp_peer_or_fw.typeof == 'external_bgp_peer':
              ref = 'external_bgp_peer_address_ref'
          else: # engine
              ref = 'fwcluster_peer_address_ref'
          self.conditions.append(
              {ref: ext_bgp_peer_or_fw.href,
               'rank': rank,
               'type': 'peer_address'})
docs: Add a peer address. Peer address types are ExternalBGPPeer
          or Engine.
          
          :raises ElementNotFound: If element specified does not exist