docs: private String genReference(String id, ElementDefinition.TypeRefComponent typ) {
      ST shex_ref = tmplt(REFERENCE_DEFN_TEMPLATE);
  
      String ref = getTypeName(typ);
      shex_ref.add("id", id);
      shex_ref.add("ref", ref);
      references.add(ref);
      return shex_ref.render();
    }