/*
 * call-seq:
 *  [](i)
 *
 * Get the node at index +i+
 */
static VALUE index_at(VALUE self, VALUE number)
{
  int i = NUM2INT(number);
  xmlNodeSetPtr node_set;
  Data_Get_Struct(self, xmlNodeSet, node_set);

  if(i >= node_set->nodeNr || abs(i) > node_set->nodeNr)
    return Qnil;

  if(i < 0)
    i = i + node_set->nodeNr;

  return Nokogiri_wrap_xml_node(node_set->nodeTab[i]);
}