code: @Nonnull
      public Section addSection(String title, Format format, String content) {
          return add(null, title, format, content);
      }
docs: Adds a custom section, that isn't related to any element in the model.
  
  @param title             the section title
  @param format    the {@link Format} of the documentation content
  @param content   a String containing the documentation content
  @return           a documentation {@link Section}