anchor.diff:        || experimentalFpMbStatsSupport
         || experimentalEmulateHardwareSupport)}-experimental"
     ] # Experimental features
  -    ++ optional experimentalSpatialSvcSupport "--enable-spatial-svc"
  +    ++ optional experimentalSpatialSvcSupport "--enable-spatial-svc"  # Removed in 1.8.x
       ++ optional experimentalFpMbStatsSupport "--enable-fp-mb-stats"
       ++ optional experimentalEmulateHardwareSupport "--enable-emulate-hardware"
  +    ++ optional experimentalNonGreedyMvSupport "--enable-non-greedy-mv"
  +    ++ optional experimentalMlVarPartitionSupport "--enable-ml-var-partition"  # Removed in 1.9.x
       ++ optional experimentalMiscFixes "--enable-misc-fixes";
   
     meta = with lib; {
  
positive.code:     };
      # master
      "1.999" = {
        fetchzipversion = 5;
        version = "2018-01-12";
        rev = "f915e6d4afafabed8281b172f93502acbe101f3a";
        sha256 = "137725fe8510ca855da293bd1794a9500aeaf90d34c01e323f992af560dc6769";
      };
    };
    source = sources."${channel}";
  
negative.code: , experimentalSpatialSvcSupport ? false # Spatial scalable video coding
  , experimentalFpMbStatsSupport ? false
  , experimentalEmulateHardwareSupport ? false
  , experimentalNonGreedyMvSupport ? false
  , experimentalMlVarPartitionSupport ? false
  , experimentalMiscFixes ? false
  
  , channel
  