docs: public static Set<String> calcPropertySourceNames(String prefix, Set<String> activeNames, String separator) {
          Set<String> propertySourceNames;
          if (prefix.contains(separator)) {
  
              String[] tokens = prefix.split(separator);
              if (tokens.length == 1) {
                  propertySourceNames = Collections.singleton(tokens[0]);
              } else {
                  String name = tokens[0];
                  Set<String> newSet = new HashSet<>(tokens.length - 1);
                  for (int j = 1; j < tokens.length; j++) {
                      String envName = tokens[j];
                      if (!activeNames.contains(envName)) {
                          return Collections.emptySet();
                      }
                      newSet.add(name + '[' + envName + ']');
                  }
                  propertySourceNames = newSet;
              }
          } else {
              propertySourceNames = Collections.singleton(prefix);
          }
          return propertySourceNames;
      }