public PageSizeAggregate(IEnumerable<Size> sizes)
                    : base()
                {
                    this._count = 0;

                    foreach (Size s in sizes)
                    {
                        Multiple.Add(s);
                        this._count++;
                    }

                    if (this._count <= 0)
                        throw new ArgumentOutOfRangeException("sizes", "sizes must have at least one entry");
                }