anchor.diff:            echo "Adding $item..."
             rsync -ak --chown=0:0 $item/ layer/
           done
  +
  +        chmod ug+w layer
         '';
   
         postMount = ''
  
positive.code:     # How much disk to allocate for the temporary virtual machine.
      diskSize ? 1024,
      # Commands (bash) to run on the layer; these do not require sudo.
      extraCommands ? "", uid ? 0, gid ? 0
    }:
      # Generate an executable script from the `runAsRoot` text.
      let runAsRootScript = shellScript "run-as-root.sh" runAsRoot;
  
negative.code:         echo "No contents to add to layer."
        fi
  
        chmod ug+w layer
  
        if [[ -n $extraCommands ]]; then
          (cd layer; eval "$extraCommands")
        fi
  