anchor.diff:  
     barStr = {
       id, fonts, mode, hiddenState, position, workspaceButtons,
  -    workspaceNumbers, command, statusCommand, colors, ...
  +    workspaceNumbers, command, statusCommand, colors, trayOutput, ...
     }: ''
       bar {
         ${optionalString (id != null) "id ${id}"}
  
positive.code:       i3bar_command ${command}
        workspace_buttons ${if workspaceButtons then "yes" else "no"}
        strip_workspace_numbers ${if !workspaceNumbers then "yes" else "no"}
        colors {
          background ${colors.background}
          statusline ${colors.statusline}
  
negative.code: 
            See <link xlink:href="https://i3wm.org/docs/userguide.html#_colors"/>.
          '';
        };
  
        trayOutput = mkOption {
          type = types.string;
          default = "primary";
          description = "Where to output tray.";
        };
      };
    };
  