setCurve( index, curveNo ) {

		if ( isNaN( curveNo ) ) throw Error( 'InstancedFlow: Curve index being set is Not a Number (NaN).' );
		this.whichCurve[ index ] = curveNo;
		this.writeChanges( index );

	}
Select which curve to use for an element.

@param {number} index - The index of the instanced element to update.
@param {number} curveNo - The index of the curve it should use.