docs: def _send_ffcs(self, region, core_mask, fr):
          """Send a flood-fill core select packet.
  
          This packet was added in a patched SC&MP 1.34*. Each packet includes a
          region and a core mask; every core that is in the region ORs the core
          mask with a mask it stores locally. On receiving a flood-fill end (FFE)
          packet the application is loaded to the cores specified by this
          composed core mask.
  
          FFCS packets should be sent in ascending order of
          `(region << 18) | core`.
  
          * See https://bitbucket.org/mundya/scamp/branch/new-ff2
          """
          arg1 = (NNCommands.flood_fill_core_select << 24) | core_mask
          arg2 = region
          self._send_scp(255, 255, 0, SCPCommands.nearest_neighbour_packet,
                         arg1, arg2, fr)