bool this[
	int index
] { get; set; }

Property Extended ( _
	index As Integer _
) As Boolean
	Get
	Set

property bool Extended[int index] {
	bool get (int index);
	void set (int index, bool value);
}

Property index must be 0 or 1 to indicate two ends, otherwise exceptions will be thrown. For beams, if the beam extension status is changed, other status such as the symbolic extension status, miter status, miter locked status, and other beams extension status will be changed automatically at the same time. This change can protect that a join can have up to two extended beams, if there are two extended beams at the join, they shall be mitered.