@Override
  public void addSelectedContent(final @NotNull Content content) {
    if (!checkSelectionChangeShouldBeProcessed(content, false)) return;

    if (getIndexOfContent(content) == -1) {
      throw new IllegalArgumentException("content not found: " + content);
    }
    if (!isSelected(content)) {
      mySelection.add(content);
      fireSelectionChanged(content, ContentManagerEvent.ContentOperation.add);
    }
  }
@Override
  public void addSelectedContent(final @NotNull Content content)