/// <summary>
/// Gets all directives of the specified type that exist in the plan.
/// </summary>
/// <typeparam name="TDirective">The type of directive.</typeparam>
/// <returns>A series of directives of the specified type.</returns>
public IEnumerable <TDirective> GetAll <TDirective>()
where TDirective : IDirective
{
return(Directives.OfType <TDirective>());
}
