code: public Parse cloneRoot(final Parse node, final int parseIndex) {
      final Parse c = (Parse) this.clone();
      final Parse fc = c.parts.get(parseIndex);
      c.parts.set(parseIndex, fc.clone(node));
      return c;
    }
docs: Clones the right frontier of this root parse up to and including the
  specified node.
  
  @param node
  The last node in the right frontier of the parse tree which should
  be cloned.
  @param parseIndex
  The child index of the parse for this root node.
  @return A clone of this root parse and its right frontier up to and
  including the specified node.