anchor.diff:              ;;
             --branch=*)
               branch="''${flag#*=}"
  +            ;;
  +          --use-stable-version)
  +            use_stable_version=1
  +            ;;
  +          --tag-prefix=*)
  +            tag_prefix="''${flag#*=}"
               ;;
             *)
               echo "$0: unknown option ‘''${flag}’"
  
positive.code:     pushd "$tmpdir"
      commit_date="$(${git}/bin/git show -s --pretty='format:%cs')"
      commit_sha="$(${git}/bin/git show -s --pretty='format:%H')"
      popd
      ${coreutils}/bin/rm -rf "$tmpdir"
  
      # update the nix expression
      ${common-updater-scripts}/bin/update-source-version \
          "$UPDATE_NIX_ATTR_PATH" \
          "unstable-$commit_date" \
          --rev="$commit_sha"
    '';
  
  
negative.code: # commit.
  { url ? null # The git url, if empty it will be set to src.url
  , branch ? null
  , stableVersion ? false # Use version format according to RFC 107 (i.e. LAST_TAG+date=YYYY-MM-DD)
  , tagPrefix ? "" # strip this prefix from a tag name when using stable version
  }:
  
  let
  