Alias for [page:EllipseCurve]
See the [page:EllipseCurve] class for common properties.
Used to check whether this or derived classes are ArcCurves. Default is *true*.
You should not change this, as it used internally for optimisation.
[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]