/// <summary>
/// Returns an enumerable of all handles of the specified type in the model
/// </summary>
/// <typeparam name="T">The type of entity required</typeparam>
/// <returns></returns>
public IEnumerable <XbimInstanceHandle> Handles <T>()
{
foreach (var item in cache.InstanceHandlesOfType <T>())
{
yield return(item);
}
}
