Format

    VARIANTS.
     {                                                       }
     {VARIANT [EXPRESSION IS cond-expr] .                    }
     {             [included-name-clause ]                   }
     {             [local-field-clause   ]                   } ...
     {             [structure-name-clause] ... END VARIANT . }
     {             [variants-clause      ]                   }
     {                                                       }
    END VARIANTS  .