code: public void setChild(final int index, final String label) {
      final Parse newChild = (Parse) this.parts.get(index).clone();
      newChild.setLabel(label);
      this.parts.set(index, newChild);
    }
docs: Replaces the child at the specified index with a new child with the
  specified label.
  
  @param index
  The index of the child to be replaced.
  @param label
  The label to be assigned to the new child.