@Override
    protected void onDocumentChanged1(@NotNull DocumentEvent event) {
      if (!myRangeMarker.isValid()) {
        myDocument2.setReadOnly(false);
        try {
          replaceString(myDocument2, 0, myDocument2.getTextLength(),
                        DiffBundle.message("synchronize.document.and.its.fragment.range.error"));
        }
        finally {
          myDocument2.setReadOnly(true);
        }
        return;
      }
      CharSequence newText = myDocument1.getCharsSequence().subSequence(myRangeMarker.getStartOffset(), myRangeMarker.getEndOffset());
      replaceString(myDocument2, 0, myDocument2.getTextLength(), newText);
    }
@Override
    protected void onDocumentChanged1(@NotNull DocumentEvent event)