/// <summary>
/// Specify explicit ordering of children by Id.
/// Id's not corresponding to children will be ignored.
/// Not all children need to be specified. However, specified children take precedence;
/// unspecified children will be moved (if necessary) behind the specified ones.
/// </summary>
/// <param name="preferredOrder"></param>
public virtual void OrderChildren(params TId[] preferredOrder)
{
var existingOrder = ChildrenList.Select(n => n.Id).ToArray();
var specifiedIds = preferredOrder.Intersect(existingOrder, Definition.IdEqualityComparer);
var unspecifiedIds = existingOrder.Except(preferredOrder, Definition.IdEqualityComparer);
var orderMap =
specifiedIds.Concat(unspecifiedIds)
.Select((id, i) => new { id, i })
.ToDictionary(pair => pair.id, pair => pair.i, Definition.IdEqualityComparer);
OrderChildren(seq => seq.OrderBy(n => orderMap[n.Id]));
}