docs: public static ClientSelector labelSelector(final String labelMask) {
          return new ClientSelector() {
              @Override
              public boolean select(Client client) {
                  Set<String> labels = client.getLabels();
                  for (String label : labels) {
                      if (label.matches(labelMask)) {
                          return true;
                      }
                  }
                  return false;
              }
  
              @Override
              public String toString() {
                  return "ClientSelector{labelMask:" + labelMask + " }";
              }
          };
      }