code: public static String getAt(CharSequence self, Collection indices) {
          StringBuilder answer = new StringBuilder();
          for (Object value : indices) {
              if (value instanceof Range) {
                  answer.append(getAt(self, (Range) value));
              } else if (value instanceof Collection) {
                  answer.append(getAt(self, (Collection) value));
              } else {
                  int idx = DefaultTypeTransformation.intUnbox(value);
                  answer.append(getAt(self, idx));
              }
          }
          return answer.toString();
      }
docs: Select a List of characters from a CharSequence using a Collection
  to identify the indices to be selected.
  
  @param self    a CharSequence
  @param indices a Collection of indices
  @return a String consisting of the characters at the given indices
  @since 1.0