code: public static String getProviderInfo() {
  
          StringBuilder sb = new StringBuilder(128);
          sb.append(Timezone.class.getName());
          sb.append(":[default-provider=");
          sb.append(DEFAULT_PROVIDER.getName());
          sb.append(", registered={");
  
          for (String key : PROVIDERS.keySet()) {
              ZoneModelProvider provider = PROVIDERS.get(key);
              if (provider != null) { // defensive against parallel threads
                  sb.append("(name=");
                  sb.append(provider.getName());
  
                  String location = provider.getLocation();
  
                  if (!location.isEmpty()) {
                      sb.append(",location=");
                      sb.append(location);
                  }
  
                  String version = provider.getVersion();
  
                  if (!version.isEmpty()) {
                      sb.append(",version=");
                      sb.append(version);
                  }
  
                  sb.append(')');
              }
          }
  
          sb.append("}]");
          return sb.toString();
  
      }
docs: /*[deutsch]
  <p>Beschreibt alle registrierten {@code ZoneModelProvider}-Instanzen
  mit Namen und optional Ort und Version. </p>
  
  @return  String