docs: final void writeIonVersionMarker(SymbolTable systemSymtab)
          throws IOException
      {
          if (getDepth() != 0)
          {
              String message =
                  "Ion Version Markers are only valid at the top level of a " +
                  "data stream";
              throw new IllegalStateException(message);
          }
          assert systemSymtab.isSystemTable();
  
          if (! SystemSymbols.ION_1_0.equals(systemSymtab.getIonVersionId()))
          {
              String message = "This library only supports Ion 1.0";
              throw new UnsupportedOperationException(message);
          }
  
          if (shouldWriteIvm())
          {
              _initial_ivm_handling = null;
  
              writeIonVersionMarkerAsIs(systemSymtab);
  
              _previous_value_was_ivm = true;
          }
  
          _symbol_table = systemSymtab;
      }