docs: public void putIndexedFixedProperties(String key, List<String> subKeys, List<List<String>> subKeyValues) {
  		checkNotNull(key);
  		checkNotNull(subKeys);
  		checkNotNull(subKeyValues);
  		for (int idx = 0; idx < subKeyValues.size(); idx++) {
  			final List<String> values = subKeyValues.get(idx);
  			if (values == null || values.size() != subKeys.size()) {
  				throw new ValidationException("Values must have same arity as keys.");
  			}
  			for (int keyIdx = 0; keyIdx < values.size(); keyIdx++) {
  				put(key + '.' + idx + '.' + subKeys.get(keyIdx), values.get(keyIdx));
  			}
  		}
  	}