code: @Trivial
      private static final String getUID(String configDisplayId, String id) {
          return id == null || configDisplayId.matches(".*/.*\\[.*\\].*") ? configDisplayId : id;
      }
docs: Compute the unique identifier from the id and config.displayId.
  If a top level configuration element has an id, the id is the unique identifier.
  Otherwise, the config.displayId is the unique identifier.
  
  @param configDisplayId config.displayId of configuration element.
  @param id              id of configuration element. Null if none.
  @return the unique identifier (uid)