code: public void setElements(List<AstNode> elements) {
          if (elements == null) {
              this.elements = null;
          } else {
              if (this.elements != null)
                  this.elements.clear();
              for (AstNode e : elements)
                  addElement(e);
          }
      }
docs: Sets the element list, and sets each element's parent to this node.
  @param elements the element list.  Can be {@code null}.