Format
    {         [[ EXPRESSION  IS cond-expr ]         ]               }
    {         [[                          ] .       ]               }
    {         [[ NOEXPRESSION             ]         ]               }
    {         [[ DELETE name . ]  ...               ]               }
    {         [[ included-name-change-clause ]      ]               }
    {         [[                             ]      ]               }
    { VARIANT [[ local-field-clause          ]      ] END VARIANT . }
    {         [[                             ]      ]               }
    {         [[ record-change-clause        ] ...  ]               }
    {         [[                             ]      ]               }
    {         [[ structure-change-clause     ]      ]               }
    {         [[ variants-change-clause      ]      ]               }
    {         [                                     ]               }