public ShapeNode(SpanFactory <ShapeNode> spanFactory, FeatureStruct fs)
{
_spanFactory = spanFactory;
_ann = new Annotation <ShapeNode>(spanFactory.Create(this), fs);
_tag = int.MinValue;
}
internal Span(SpanFactory <TOffset> spanFactory, TOffset start, TOffset end)
{
_spanFactory = spanFactory;
_start = start;
_end = end;
}