docs: private void open_local_symbol_table_copy()
      {
          assert(! symbol_table_being_collected());
  
          _symbol_table_value = _symtab_value_factory.newEmptyStruct();
  
          SymbolToken[] anns = _system_writer.getTypeAnnotationSymbols();
          _system_writer.clearAnnotations();
  
          _symbol_table_value.setTypeAnnotationSymbols(anns);
  
          _current_writer = new IonWriterSystemTree(activeSystemSymbolTable(),
                                                    _catalog,
                                                    _symbol_table_value,
                                                    null /* initialIvmHandling */);
      }