code: public static List<Number> findIndexValues(Object self, Number startIndex, Closure condition) {
          return findIndexValues(InvokerHelper.asIterator(self), startIndex, condition);
      }
docs: Iterates over the elements of an aggregate of items, starting from
  a specified startIndex, and returns the index values of the items that match
  the condition specified in the closure.
  
  @param self       the iteration object over which to iterate
  @param startIndex start matching from this index
  @param condition  the matching condition
  @return a list of numbers corresponding to the index values of all matched objects
  @since 1.5.2