code: private void addContentTypeRecursively(ContentType contentType) {
  
      addContentType(contentType);
      for (ContentType child : contentType.getChildren()) {
        addContentTypeRecursively(child);
      }
    }
docs: This method walks down the tree of {@link ContentType}s recursively and {@link #addContentType(ContentType) adds}
  them to this manager.
  
  @param contentType is the {@link ContentType} to register recursively (via its {@link ContentType#getChildren()
  children}).