code: @Override
      public List<String> sources() {
          List<String> sources = new ArrayList<>();
          for (int i = 0; i < this._sections.size(); i++) {
              for (int j = 0; j < this._sections.get(i).consumer.sources().size(); j++) {
                  sources.add(this._sections.get(i).consumer.sources().get(j));
              }
          }
          return sources;
      }
docs: The list of original sources.