docs: private StringBuilder makeDescription(Collection<Relation<?>> relations, DBIDRef id) {
      StringBuilder buf = new StringBuilder();
      for(Relation<?> rel : relations) {
        Object o = rel.get(id);
        if(o == null) {
          continue;
        }
        String s = o.toString();
        // FIXME: strip html characters
        if(s != null) {
          if(buf.length() > 0) {
            buf.append("<br />");
          }
          buf.append(s);
        }
      }
      return buf;
    }