code: public List<Tag> getRootTags()
      {
          return this.definedTags.values().stream()
                      .filter(Tag::isRoot)
                      .collect(Collectors.toList());
      }
docs: Returns the tags that were root in the definition files. These serve as entry point shortcuts when browsing the graph. We could reduce this to
  just fewer as the root tags may be connected through parents="...".