public void Add(string anchor_name, YamlNode node)
{
if ( Items.ContainsKey(anchor_name) ) {
// override an existing anchor
ItemsToRewind.Push(new RewindInfo(anchor_name, this[anchor_name]));
Items[anchor_name] = node;
} else {
ItemsToRewind.Push(new RewindInfo(anchor_name, null));
Items.Add(anchor_name, node);
}
}