<!-- NEW4 — TEST 4 · THE QUILT · part 108 -->
 to this plane.
	 */
	set( normal, constant ) {

		this.normal.copy( normal );
		this.constant = constant;

		return this;

	}

	/**
	 * Sets the plane components by defining `x`, `y`, `z` as the
	 * plane normal and `w` as the constant.
	 *
	 * @param {number} x - The value for the normal's x component.
	 * @param {number} y - The value for the normal's y component.
	 * @param {number} z - The value for the normal's z component.
	 * @param {number} w - The constant value.
	 * @return {Plane} A reference to this plane.
	 */
	setComponents( x, y, z, w ) {

		this.normal.set( x, y, z );
		this.constant = w;

		return this;

	}

	/**
	 * Sets the plane from the given normal and coplanar point (that is a point
	 * that lies onto the plane).
	 *
	 * @param {Vector3} normal - The normal.
	 * @param {Vector3} point - A coplanar point.
	 * @return {Plane} A reference to this plane.
	 */
	setFromNormalAndCoplanarPoint( normal, point ) {

		this.normal.copy( normal );
		this.constant = - point.dot( this.normal );

		return this;

	}

	/**
	 * Sets the plane from three coplanar points. The winding order is
	 * assumed to be counter-clockwise, and determines the direction of
	 * the plane normal.
	 *
	 * @param {Vector3} a - The first coplanar point.
	 * @param {Vector3} b - The second coplanar point.
	 * @param {Vector3} c - The third coplanar point.
	 * @return {Plane} A reference to this plane.
	 */
	setFromCoplanarPoints( a, b, c ) {

		const normal = _vector1.subVectors( c, b ).cross( _vector2.subVectors( a, b ) ).normalize();

		// Q: should an error be thrown if normal is zero (e.g. degenerate plane)?

		this.setFromNormalAndCoplanarPoint( normal, a );

		return this;

	}

	/**
	 * Copies the values of the given plane to this instance.
	 *
	 * @param {Plane} plane - The plane to copy.
	 * @return {Plane} A reference to this plane.
	 */
	copy( plane ) {

		this.normal.copy( plane.normal );
		this.constant = plane.constant;

		return this;

	}

	/**
	 * Normalizes the plane normal and adjusts the constant accordingly.
	 *
	 * @return {Plane} A reference to this plane.
	 */
	normalize() {

		// Note: will lead to a divide by zero if the plane is invalid.

		const inverseNormalLength = 1.0 / this.normal.length();
		this.normal.multiplyScalar( inverseNormalLength );
		this.constant *= inverseNormalLength;

		return this;

	}

	/**
	 * Negates both the plane normal and the constant.
	 *
	 * @return {Plane} A reference to this plane.
	 */
	negate() {

		this.constant *= -1;
		this.normal.negate();

		return this;

	}

	/**
	 * Returns the signed distance from the given point to this plane.
	 *
	 * @param {Vector3} point - The point to compute the distance for.
	 * @return {number} The signed distance.
	 */
	distanceToPoint( point ) {

		return this.normal.dot( point ) + this.constant;

	}

	/**
	 * Returns the signed distance from the given sphere to this plane.
	 *
	 * @param {Sphere} sphere - The sphere to compute the distance for.
	 * @return {number} The signed distance.
	 */
	distanceToSphere( sphere ) {

		return this.distanceToPoint( sphere.center ) - sphere.radius;

	}

	/**
	 * Projects a the given point onto the plane.
	 *
	 * @param {Vector3} point - The point to project.
	 * @param {Vector3} target - The target vector that is used to store the method's result.
	 * @return {Vector3} The projected point on the plane.
	 */
	projectPoint( point, target ) {

		return target.copy( point ).addScaledVector( this.normal, - this.distanceToPoint( point ) );

	}

	/**
	 * Returns the intersection point of the passed line and the plane. Returns
	 * `null` if the line does not intersect. Returns the line's starting point if
	 * the line is coplanar with the plane.
	 *
	 * @param {Line3} line - The line to compute the intersection for.
	 * @param {Vector3} target - The target vector that is used to store the method's result.
	 * @param {boolean} [clampToLine=true] - Whether to clamp the intersection to the line segment.
	 * @return {?Vector3} The intersection point. Returns `null` if no intersection is detected.
	 */
	intersectLine( line, target, clampToLine = true ) {

		const direction = line.delta( _vector1 );

		const denominator = this.normal.dot( direction );

		if ( denominator === 0 ) {

			// line is coplanar, return origin
			if ( this.distanceToPoint( line.start ) === 0 ) {

				return target.copy( line.start );

			}

			// Unsure if this is the correct method to handle this case.
			return null;

		}

		const t = - ( line.start.dot( this.normal ) + this.constant ) / denominator;

		if ( ( clampToLine === true ) && ( t < 0 || t > 1 ) ) {

			return null;

		}

		return target.copy( line.start ).addScaledVector( direction, t );

	}

	/**
	 * Returns `true` if the given line segment intersects with (passes through) the plane.
	 *
	 * @param {Line3} line - The line to test.
	 * @return {boolean} Whether the given line segment intersects with the plane or not.
	 */