void onPlaceholderTextChanged(FoldRegionImpl region) {
    if (!myIsBatchFoldingProcessing) {
      LOG.error("Fold regions must be changed inside batchFoldProcessing() only");
    }
    onFoldProcessingStart();
    myEditor.myView.invalidateFoldRegionLayout(region);
    onFoldRegionStateChange(region);
  }
void onPlaceholderTextChanged(FoldRegionImpl region)