diff --git a/font-src/gen/caching/index.mjs b/font-src/gen/caching/index.mjs
index 63d83b19d..53017a785 100644
--- a/font-src/gen/caching/index.mjs
+++ b/font-src/gen/caching/index.mjs
@@ -3,7 +3,7 @@ import zlib from "zlib";
 
 import { encode, decode } from "@msgpack/msgpack";
 
-const Edition = 24;
+const Edition = 25;
 const MAX_AGE = 16;
 class GfEntry {
 	constructor(age, value) {
diff --git a/font-src/glyphs/common/shapes.ptl b/font-src/glyphs/common/shapes.ptl
index 2662ce20d..ef5b5c0a3 100644
--- a/font-src/glyphs/common/shapes.ptl
+++ b/font-src/glyphs/common/shapes.ptl
@@ -4,6 +4,7 @@ import [Transform] from"../../support/geometry/transform.mjs"
 
 import [mix linreg clamp fallback] from"../../support/utils.mjs"
 import [Radical] from"../../support/gr.mjs"
+import [Interpolator] from"../../support/geometry/spiro-control.mjs"
 
 glyph-module
 
@@ -513,25 +514,12 @@ glyph-block CommonShapes : begin
 		return : HookShape before after false args.y args.tight args.sw args.swItalicAdj args.noAdjTerminalY
 
 	glyph-block-export hookstart
-	define [hookstart] : params [y tight sw swItalicAdj noAdjTerminalY] : return {
-		.type 'interpolate'
-		.blender hookStartBlender
-		.y y
-		.tight tight
-		.sw sw
-		.swItalicAdj swItalicAdj
-		.noAdjTerminalY noAdjTerminalY
-	}
+	define [hookstart] : params [y tight sw swItalicAdj noAdjTerminalY] : begin
+		return : Interpolator hookStartBlender : object y tight sw swItalicAdj noAdjTerminalY
+
 	glyph-block-export hookend
-	define [hookend] : params [y tight sw swItalicAdj noAdjTerminalY] : return {
-		.type 'interpolate'
-		.blender hookEndBlender
-		.y y
-		.tight tight
-		.sw sw
-		.swItalicAdj swItalicAdj
-		.noAdjTerminalY noAdjTerminalY
-	}
+	define [hookend] : params [y tight sw swItalicAdj noAdjTerminalY] : begin
+		return : Interpolator hookEndBlender : object y tight sw swItalicAdj noAdjTerminalY
 
 	glyph-block-export Ungizmo
 	define [Ungizmo] : glyph-proc
diff --git a/font-src/glyphs/letter/latin/s.ptl b/font-src/glyphs/letter/latin/s.ptl
index e4bb8fd89..71a3b8e5e 100644
--- a/font-src/glyphs/letter/latin/s.ptl
+++ b/font-src/glyphs/letter/latin/s.ptl
@@ -357,7 +357,7 @@ glyph-block Letter-Latin-S : begin
 	CreateAccentedComposition 'sTildeOver' 0x1D74 's' 'tildeOverWide'
 
 	derive-composites 'SCedilla' 0x15E 'S' 'cedillaExtShapeBelowOArc'
-	derive-composites 'sCedilla' 0x15F 's' 'cedillaExtShapeBelowOArc'
+	derive-composites 'sCedilla' 0x15F 's' 'cedillaExtShapeBelowSOArc'
 
 	create-glyph 'mathbb/S' 0x1D54A : glyph-proc
 		include : MarkSet.capital
diff --git a/font-src/glyphs/marks/below.ptl b/font-src/glyphs/marks/below.ptl
index 25a80769c..d49a5ae52 100644
--- a/font-src/glyphs/marks/below.ptl
+++ b/font-src/glyphs/marks/below.ptl
@@ -54,6 +54,12 @@ glyph-block Mark-Below : begin
 		set-base-anchor 'belowBrace' markMiddle belowMarkMid
 		include : CedillaShape (Stroke + O)
 
+	create-glyph 'cedillaExtShapeBelowSOArc' : glyph-proc
+		set-width 0
+		set-mark-anchor 'below' markMiddle 0 markMiddle belowMarkStack
+		set-base-anchor 'belowBrace' markMiddle belowMarkMid
+		include : CedillaShape ([AdviceStroke2 2 3 XH] + O)
+
 	create-glyph 'cedillaBelow' 0x327 : glyph-proc
 		set-width 0
 		set-mark-anchor 'below' markMiddle 0 markMiddle belowMarkStack
diff --git a/font-src/kits/spiro-kit.mjs b/font-src/kits/spiro-kit.mjs
index fde2de5c7..e4bf98dcb 100644
--- a/font-src/kits/spiro-kit.mjs
+++ b/font-src/kits/spiro-kit.mjs
@@ -1,48 +1,62 @@
-import * as CurveUtil from "../support/geometry/curve-util.mjs";
-import { SpiroGeometry, DiSpiroGeometry } from "../support/geometry/index.mjs";
-import { BiKnotCollector } from "../support/geometry/spiro-expand.mjs";
-import { fallback, mix, bez3 } from "../support/utils.mjs";
+import { DiSpiroGeometry, SpiroGeometry } from "../support/geometry/index.mjs";
+import {
+	BiKnotCollector,
+	ControlKnot,
+	Interpolator,
+	TerminateInstruction
+} from "../support/geometry/spiro-control.mjs";
+import { bez3, fallback, mix } from "../support/utils.mjs";
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
-class DispiroImpl {
+
+class SpiroImplBase {
 	constructor(bindings, args) {
 		this.bindings = bindings;
 		this.args = args;
 	}
-	applyToGlyph(glyph) {
+
+	createCollector(glyph) {
 		const gizmo = glyph.gizmo || this.bindings.GlobalTransform;
-		const collector = new BiKnotCollector(gizmo, this.bindings.Contrast);
-		const { knots, closed } = prepareSpiroKnots(this.args, collector);
-		for (const knot of knots) {
-			collector.pushKnot(knot.type, knot.x, knot.y);
-			if (knot.af) knot.af.call(collector);
-		}
-		const dsp = new DiSpiroProxy(closed, collector, knots);
+
+		const collector = new BiKnotCollector(this.bindings.Contrast);
+		for (const control of this.args) collector.add(control);
+		collector.unwrap();
+
+		return { gizmo, collector };
+	}
+}
+
+class DispiroImpl extends SpiroImplBase {
+	constructor(bindings, args) {
+		super(bindings, args);
+	}
+	applyToGlyph(glyph) {
+		const { gizmo, collector } = this.createCollector(glyph);
+		const dsp = new DiSpiroProxy(gizmo, collector);
 		glyph.includeGeometry(dsp.geometry);
 		return dsp;
 	}
 }
-class SpiroOutlineImpl {
+class SpiroOutlineImpl extends SpiroImplBase {
 	constructor(bindings, args) {
-		this.bindings = bindings;
-		this.args = args;
+		super(bindings, args);
 	}
 	applyToGlyph(glyph) {
-		const gizmo = glyph.gizmo || this.bindings.GlobalTransform;
-		const g = new CurveUtil.BezToContoursSink(gizmo);
-		const { knots, closed } = prepareSpiroKnots(this.args, g);
-		return glyph.includeGeometry(new SpiroGeometry(gizmo, closed, knots));
+		const { gizmo, collector } = this.createCollector(glyph);
+		return glyph.includeGeometry(
+			new SpiroGeometry(gizmo, collector.closed, collector.controls)
+		);
 	}
 }
 class DiSpiroProxy {
-	constructor(closed, collector, origKnots) {
+	constructor(gizmo, collector) {
 		this.geometry = new DiSpiroGeometry(
-			collector.gizmo,
+			gizmo,
 			collector.contrast,
-			closed,
-			collector.controlKnots
+			collector.closed,
+			collector.controls
 		);
-		this.m_origKnots = origKnots;
+		this.m_origKnots = collector.controls;
 	}
 	get knots() {
 		return this.m_origKnots;
@@ -54,69 +68,23 @@ class DiSpiroProxy {
 		return this.geometry.expand().rhsUntransformed;
 	}
 }
-function prepareSpiroKnots(_knots, s) {
-	let knots = [..._knots];
-	while (knots[0] && knots[0] instanceof Function) {
-		knots[0].call(s);
-		knots.splice(0, 1);
-	}
-	const closed = dropTailKnot(knots);
-	knots = flatten(s, knots);
-	return { knots, closed };
-}
-function dropTailKnot(knots) {
-	let last = knots[knots.length - 1];
-	if (last && (last.type === "close" || last.type === "end")) {
-		knots.length = knots.length - 1;
-		return last.type === "close";
-	} else {
-		return false;
-	}
-}
-function flatten(s, knots0) {
-	let knots = [];
-	flattenImpl(knots, knots0);
-	let unwrapped = false;
-	for (let j = 0; j < knots.length; j = j + 1)
-		if (knots[j] && knots[j].type === "interpolate") {
-			const kBefore = knots[nCyclic(j - 1, knots.length)];
-			const kAfter = knots[nCyclic(j + 1, knots.length)];
-			knots[j] = knots[j].blender(kBefore, kAfter, knots[j]);
-			unwrapped = true;
-		}
-	if (unwrapped) return flatten(s, knots);
-	return knots;
-}
-function flattenImpl(sink, knots) {
-	for (const p of knots) {
-		if (p instanceof Array) flattenImpl(sink, p);
-		else sink.push(p);
-	}
-}
-function nCyclic(p, n) {
-	return (p + n + n) % n;
-}
+
 export function SetupBuilders(bindings) {
-	const { Contrast, GlobalTransform, Stroke, Superness } = bindings;
-	function validateCoord(x) {
-		if (!isFinite(x)) throw new TypeError("NaN detected");
-		return x;
-	}
+	const { Stroke, Superness } = bindings;
 	function KnotType(type) {
-		return (x, y, f) => ({
-			type,
-			x: validateCoord(x),
-			y: validateCoord(y),
-			af: f
-		});
+		return (x, y, f) => {
+			if (!isFinite(x)) throw new TypeError("NaN detected for X");
+			if (!isFinite(y)) throw new TypeError("NaN detected for Y");
+			return new ControlKnot(type, x, y, f);
+		};
 	}
 	const g4 = KnotType("g4");
 	const g2 = KnotType("g2");
 	const corner = KnotType("corner");
 	const flat = KnotType("left");
 	const curl = KnotType("right");
-	const close = f => ({ type: "close", af: f });
-	const end = f => ({ type: "end", af: f });
+	const close = f => new TerminateInstruction("close", f);
+	const end = f => new TerminateInstruction("end", f);
 	const straight = { l: flat, r: curl };
 	{
 		let directions = [
@@ -148,9 +116,13 @@ export function SetupBuilders(bindings) {
 			}
 		}
 	}
+
 	function widths(l, r) {
 		return function () {
-			return this.setWidth ? this.setWidth(validateCoord(l), validateCoord(r)) : void 0;
+			if (!isFinite(l)) throw new TypeError("NaN detected for left width");
+			if (!isFinite(r)) throw new TypeError("NaN detected for right width");
+
+			if (this.setWidth) this.setWidth(l, r);
 		};
 	}
 	widths.lhs = function (w) {
@@ -162,46 +134,49 @@ export function SetupBuilders(bindings) {
 	widths.center = function (w) {
 		return widths(fallback(w, Stroke) / 2, fallback(w, Stroke) / 2);
 	};
+
 	function heading(d) {
 		return function () {
-			return this.headsTo ? this.headsTo(d) : void 0;
+			if (this.headsTo) this.headsTo(d);
 		};
 	}
 	widths.heading = function (l, r, d) {
 		return function () {
 			if (this.setWidth) this.setWidth(l, r);
-			return this.headsTo ? this.headsTo(d) : void 0;
+			if (this.headsTo) this.headsTo(d);
 		};
 	};
 	widths.lhs.heading = function (w, d) {
 		return function () {
 			if (this.setWidth) this.setWidth(fallback(w, Stroke), 0);
-			return this.headsTo ? this.headsTo(d) : void 0;
+			if (this.headsTo) this.headsTo(d);
 		};
 	};
 	widths.rhs.heading = function (w, d) {
 		return function () {
 			if (this.setWidth) this.setWidth(0, fallback(w, Stroke));
-			return this.headsTo ? this.headsTo(d) : void 0;
+			if (this.headsTo) this.headsTo(d);
 		};
 	};
 	widths.center.heading = function (w, d) {
 		return function () {
 			if (this.setWidth) this.setWidth(fallback(w, Stroke) / 2, fallback(w, Stroke) / 2);
-			return this.headsTo ? this.headsTo(d) : void 0;
+			if (this.headsTo) this.headsTo(d);
 		};
 	};
+
 	function disableContrast() {
 		return function () {
-			return (this.contrast = 1);
+			if (this.setContrast) this.setContrast(1);
 		};
 	}
 	function unimportant() {
-		return this.setUnimportant ? this.setUnimportant() : void 0;
+		if (this.setUnimportant) this.setUnimportant(1);
 	}
 	function important() {
 		return void 0;
 	}
+
 	function afInterpolate(before, after, args) {
 		return g4(
 			mix(before.x, after.x, args.rx),
@@ -272,23 +247,24 @@ export function SetupBuilders(bindings) {
 	}
 
 	function alsoThru(rx, ry, raf) {
-		return { type: "interpolate", rx, ry, raf, blender: afInterpolate };
+		return Interpolator(afInterpolate, { rx, ry, raf });
 	}
 	alsoThru.withOffset = function (rx, ry, deltaX, deltaY, raf) {
-		return { type: "interpolate", rx, ry, deltaX, deltaY, raf, blender: afInterpolateDelta };
+		return Interpolator(afInterpolateDelta, { rx, ry, deltaX, deltaY, raf });
 	};
 	alsoThru.g2 = function (rx, ry, raf) {
-		return { type: "interpolate", rx, ry, raf, blender: afInterpolateG2 };
+		return Interpolator(afInterpolateG2, { rx, ry, raf });
 	};
-	function alsoThruThem(es, raf, ty) {
-		return { type: "interpolate", rs: es, raf, ty, blender: afInterpolateThem };
+	function alsoThruThem(rs, raf, ty) {
+		return Interpolator(afInterpolateThem, { rs, raf, ty });
 	}
-	alsoThruThem.withOffset = function (es, raf, ty) {
-		return { type: "interpolate", rs: es, raf, ty, blender: afInterpolateThemWithDelta };
+	alsoThruThem.withOffset = function (rs, raf, ty) {
+		return Interpolator(afInterpolateThemWithDelta, { rs, raf, ty });
 	};
-	alsoThruThem.fromTWithOffset = function (es, raf, ty) {
-		return { type: "interpolate", rs: es, raf, ty, blender: afInterpolateThemFromTWithDelta };
+	alsoThruThem.fromTWithOffset = function (rs, raf, ty) {
+		return Interpolator(afInterpolateThemFromTWithDelta, { rs, raf, ty });
 	};
+
 	function bezControlsImpl(x1, y1, x2, y2, samples, raf, ty) {
 		let rs = [];
 		for (let j = 1; j < samples; j = j + 1)
@@ -312,6 +288,7 @@ export function SetupBuilders(bindings) {
 			raf
 		);
 	}
+
 	let DEFAULT_STEPS = 6;
 	let [buildHV, buildVH] = (function (cache) {
 		function build(samples, _superness) {
diff --git a/font-src/support/geometry/index.mjs b/font-src/support/geometry/index.mjs
index 484886bb2..d79f087d4 100644
--- a/font-src/support/geometry/index.mjs
+++ b/font-src/support/geometry/index.mjs
@@ -114,8 +114,7 @@ export class SpiroGeometry extends GeometryBase {
 export class DiSpiroGeometry extends GeometryBase {
 	constructor(gizmo, contrast, closed, biKnots) {
 		super();
-		this.m_biKnots = [];
-		for (const k of biKnots) this.m_biKnots.push(k.clone());
+		this.m_biKnots = biKnots; // untransformed
 		this.m_closed = closed;
 		this.m_gizmo = gizmo;
 		this.m_contrast = contrast;
@@ -149,7 +148,7 @@ export class DiSpiroGeometry extends GeometryBase {
 			this.m_gizmo,
 			this.m_contrast,
 			this.m_closed,
-			this.m_biKnots.map(k => k.clone())
+			this.m_biKnots
 		);
 		expander.initializeNormals();
 		expander.iterateNormals();
diff --git a/font-src/support/geometry/spiro-control.mjs b/font-src/support/geometry/spiro-control.mjs
new file mode 100644
index 000000000..457b913f9
--- /dev/null
+++ b/font-src/support/geometry/spiro-control.mjs
@@ -0,0 +1,188 @@
+import * as Format from "../util/formatter.mjs";
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+export class BiKnotCollector {
+	constructor(contrast) {
+		this.contrast = contrast; // stroke contrast
+		this.defaultD1 = 0; // default LHS
+		this.defaultD2 = 0; // default RHS sw
+		this.lastKnot = null; // last knot in the processed items
+
+		this.controls = []; // all the control items
+		this.closed = false; // whether the shape is closed
+		this.needsUnwrap = false; // whether there are interpolators
+		this.afterPreFunction = false; // whether we are really processing knots
+	}
+	add(c) {
+		if (c instanceof Function) {
+			if (this.afterPreFunction) throw new Error("Invalid spiro control sequence");
+			c.call(this);
+		} else if (Array.isArray(c)) {
+			for (const item of c) this.add(item);
+		} else if (c instanceof ControlKnot) {
+			this.afterPreFunction = true;
+			this.pushKnot(c);
+		} else if (c instanceof TerminateInstruction) {
+			this.afterPreFunction = true;
+			if (c.type === "close") this.closed = true;
+			c.applyTo(this);
+		} else if (c instanceof InterpolatorBase) {
+			this.afterPreFunction = true;
+			this.controls.push(c);
+			this.needsUnwrap = true;
+		} else {
+			throw new Error("Invalid spiro control type");
+		}
+	}
+	unwrap() {
+		while (this.needsUnwrap) {
+			const cs = [...this.controls];
+			this.controls.length = 0;
+			this.needsUnwrap = false;
+			this.lastKnot = null;
+			this.unwrapImpl(cs);
+		}
+		for (const item of this.controls) {
+			if (!(item instanceof BiKnot)) throw new Error("Invalid control sequence");
+			item.originalKnot = null;
+		}
+	}
+	unwrapImpl(cs) {
+		let tmp = [];
+		for (let j = 0; j < cs.length; j++) {
+			if (cs[j] instanceof InterpolatorBase) {
+				const kBefore = cs[nCyclic(j - 1, cs.length)];
+				const kAfter = cs[nCyclic(j + 1, cs.length)];
+				const blended = cs[j].blender(kBefore.originalKnot, kAfter.originalKnot, cs[j]);
+				tmp.push(blended);
+			} else {
+				tmp.push(cs[j].originalKnot);
+			}
+		}
+
+		this.add(tmp);
+	}
+
+	pushKnot(c) {
+		let k;
+		if (this.lastKnot) {
+			k = new BiKnot(c.type, c.x, c.y, this.lastKnot.d1, this.lastKnot.d2);
+		} else {
+			k = new BiKnot(c.type, c.x, c.y, this.defaultD1, this.defaultD2);
+		}
+		k.originalKnot = c;
+
+		this.controls.push(k);
+		this.lastKnot = k;
+
+		c.applyTo(this);
+	}
+	setWidth(l, r) {
+		if (this.lastKnot) {
+			this.lastKnot.d1 = l;
+			this.lastKnot.d2 = r;
+		} else {
+			this.defaultD1 = l;
+			this.defaultD2 = r;
+		}
+	}
+	headsTo(direction) {
+		if (this.lastKnot) {
+			this.lastKnot.proposedNormal = direction;
+		}
+	}
+	setUnimportant() {
+		if (this.lastKnot) {
+			this.lastKnot.unimportant = 1;
+		}
+	}
+	setContrast(c) {
+		this.contrast = c;
+	}
+}
+
+class BiKnot {
+	constructor(type, x, y, d1, d2) {
+		this.type = type;
+		this.x = x;
+		this.y = y;
+		this.d1 = d1;
+		this.d2 = d2;
+		this.origTangent = null;
+		this.proposedNormal = null;
+		this.unimportant = 0;
+		this.originalKnot = null;
+	}
+	clone() {
+		const k1 = new BiKnot(this.type, this.x, this.y, this.d1, this.d2);
+		k1.origTangent = this.origTangent;
+		k1.proposedNormal = this.proposedNormal;
+		k1.unimportant = this.unimportant;
+		return k1;
+	}
+	withGizmo(gizmo) {
+		const tfZ = gizmo.applyXY(this.x, this.y);
+		const k1 = new BiKnot(this.type, tfZ.x, tfZ.y, this.d1, this.d2);
+		k1.origTangent = this.origTangent ? gizmo.applyOffset(this.origTangent) : null;
+		k1.proposedNormal = this.proposedNormal ? gizmo.applyOffset(this.proposedNormal) : null;
+		k1.unimportant = this.unimportant;
+		return k1;
+	}
+	toShapeString() {
+		return Format.tuple(
+			this.type,
+			Format.n(this.x),
+			Format.n(this.y),
+			this.d1 == null ? "" : Format.n(this.d1),
+			this.d2 == null ? "" : Format.n(this.d2),
+			this.origTangent
+				? Format.tuple(Format.n(this.origTangent.x), Format.n(this.origTangent.y))
+				: "",
+			this.proposedNormal
+				? Format.tuple(Format.n(this.proposedNormal.x), Format.n(this.proposedNormal.y))
+				: "",
+			this.unimportant
+		);
+	}
+}
+
+function nCyclic(p, n) {
+	return (p + n + n) % n;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+export class ControlKnot {
+	constructor(type, x, y, af) {
+		this.type = type;
+		this.x = x;
+		this.y = y;
+		this.af = af;
+	}
+	applyTo(ctx) {
+		if (this.af) this.af.call(ctx);
+	}
+}
+export class TerminateInstruction {
+	constructor(type, af) {
+		this.type = type;
+		this.af = af;
+	}
+	applyTo(ctx) {
+		if (this.af) throw new Error("Unreachable");
+		// if (this.af) this.af.call(ctx);
+	}
+}
+export class InterpolatorBase {
+	constructor(blender) {
+		this.type = "interpolate";
+		this.blender = blender;
+	}
+}
+export function Interpolator(blender, restParameters) {
+	const base = new InterpolatorBase(blender);
+	const interpolator = Object.create(base);
+	for (const prop in restParameters) interpolator[prop] = restParameters[prop];
+	return interpolator;
+}
diff --git a/font-src/support/geometry/spiro-expand.mjs b/font-src/support/geometry/spiro-expand.mjs
index ccf93f432..5f05cf6f6 100644
--- a/font-src/support/geometry/spiro-expand.mjs
+++ b/font-src/support/geometry/spiro-expand.mjs
@@ -1,111 +1,39 @@
 import * as SpiroJs from "spiro";
 
-import * as Format from "../util/formatter.mjs";
 import { linreg } from "../utils.mjs";
 
-class BiKnot {
-	constructor(type, x, y, d1, d2) {
-		this.type = type;
-		this.x = x;
-		this.y = y;
-		this.d1 = d1;
-		this.d2 = d2;
-		this.origTangent = null;
-		this.proposedNormal = null;
-		this.unimportant = 0;
-	}
-	clone() {
-		const k1 = new BiKnot(this.type, this.x, this.y, this.d1, this.d2);
-		k1.origTangent = this.origTangent;
-		k1.proposedNormal = this.proposedNormal;
-		k1.unimportant = this.unimportant;
-		return k1;
-	}
-	toShapeString() {
-		return Format.tuple(
-			this.type,
-			Format.n(this.x),
-			Format.n(this.y),
-			this.d1 == null ? "" : Format.n(this.d1),
-			this.d2 == null ? "" : Format.n(this.d2),
-			this.origTangent
-				? Format.tuple(Format.n(this.origTangent.x), Format.n(this.origTangent.y))
-				: "",
-			this.proposedNormal
-				? Format.tuple(Format.n(this.proposedNormal.x), Format.n(this.proposedNormal.y))
-				: "",
-			this.unimportant
-		);
-	}
-}
-
-export class BiKnotCollector {
-	constructor(gizmo, contrast) {
-		this.gizmo = gizmo;
-		this.contrast = contrast;
-		this.controlKnots = [];
-		this.defaultD1 = 0;
-		this.defaultD2 = 0;
-	}
-	pushKnot(type, x, y) {
-		const tfZ = this.gizmo.applyXY(x, y);
-		const k0 = this.controlKnots[this.controlKnots.length - 1];
-		if (k0) {
-			this.controlKnots.push(new BiKnot(type, tfZ.x, tfZ.y, k0.d1, k0.d2));
-		} else {
-			this.controlKnots.push(new BiKnot(type, tfZ.x, tfZ.y, this.defaultD1, this.defaultD2));
-		}
-	}
-	setWidth(l, r) {
-		const k0 = this.controlKnots[this.controlKnots.length - 1];
-		if (k0) {
-			(k0.d1 = l), (k0.d2 = r);
-		} else {
-			(this.defaultD1 = l), (this.defaultD2 = r);
-		}
-	}
-	headsTo(direction) {
-		const transformedDirection = this.gizmo.applyOffset(direction);
-		const k0 = this.controlKnots[this.controlKnots.length - 1];
-		if (k0) k0.proposedNormal = transformedDirection;
-	}
-	setType(type) {
-		const k0 = this.controlKnots[this.controlKnots.length - 1];
-		if (k0) k0.type = type;
-	}
-	setUnimportant() {
-		const k0 = this.controlKnots[this.controlKnots.length - 1];
-		if (k0) k0.unimportant = 1;
-	}
-}
+///////////////////////////////////////////////////////////////////////////////////////////////////
 
 export class SpiroExpander {
-	constructor(gizmo, contrast, closed, cks) {
-		this.gizmo = gizmo;
-		this.contrast = contrast;
-		this.closed = closed;
-		this.controlKnots = cks;
+	constructor(gizmo, contrast, closed, biKnots) {
+		this.m_gizmo = gizmo;
+		this.m_contrast = contrast;
+		this.m_closed = closed;
+		this.m_biKnots = [];
+		for (const knot of biKnots) {
+			this.m_biKnots.push(knot.withGizmo(gizmo));
+		}
 	}
 	initializeNormals() {
-		const normalRectifier = new NormalRectifier(this.controlKnots, this.gizmo);
-		SpiroJs.spiroToArcsOnContext(this.controlKnots, this.closed, normalRectifier);
+		const normalRectifier = new NormalRectifier(this.m_biKnots, this.m_gizmo);
+		SpiroJs.spiroToArcsOnContext(this.m_biKnots, this.m_closed, normalRectifier);
 	}
 	iterateNormals() {
 		const centerBone = this.getPass2Knots();
-		const normalRectifier = new NormalRectifier(this.controlKnots, this.gizmo);
-		SpiroJs.spiroToArcsOnContext(centerBone, this.closed, normalRectifier);
+		const normalRectifier = new NormalRectifier(this.m_biKnots, this.m_gizmo);
+		SpiroJs.spiroToArcsOnContext(centerBone, this.m_closed, normalRectifier);
 	}
 	getPass2Knots() {
-		const expanded = this.expand(this.contrast);
+		const expanded = this.expand(this.m_contrast);
 		const middles = [];
-		for (let j = 0; j < this.controlKnots.length; j++) {
-			const lhs = this.gizmo.unapply(expanded.lhs[j]);
-			const rhs = this.gizmo.unapply(expanded.rhs[j]);
+		for (let j = 0; j < this.m_biKnots.length; j++) {
+			const lhs = this.m_gizmo.unapply(expanded.lhs[j]);
+			const rhs = this.m_gizmo.unapply(expanded.rhs[j]);
 			middles[j] = {
 				x: 0.5 * (lhs.x + rhs.x),
 				y: 0.5 * (lhs.y + rhs.y),
-				type: this.controlKnots[j].type,
-				unimportant: this.controlKnots[j].unimportant
+				type: this.m_biKnots[j].type,
+				unimportant: this.m_biKnots[j].unimportant
 			};
 		}
 		return middles;
@@ -114,8 +42,8 @@ export class SpiroExpander {
 		const lhs = [],
 			rhs = [];
 		// Initialize knots
-		for (let j = 0; j < this.controlKnots.length; j++) {
-			const knot = this.controlKnots[j];
+		for (let j = 0; j < this.m_biKnots.length; j++) {
+			const knot = this.m_biKnots[j];
 			lhs[j] = {
 				type: knot.type,
 				unimportant: knot.unimportant,
@@ -130,16 +58,16 @@ export class SpiroExpander {
 			};
 		}
 		// Create important knots
-		for (let j = 0; j < this.controlKnots.length; j++) {
-			const knot = this.controlKnots[j];
+		for (let j = 0; j < this.m_biKnots.length; j++) {
+			const knot = this.m_biKnots[j];
 			if (knot.unimportant) continue;
 			let dx, dy;
 			if (knot.proposedNormal) {
 				dx = knot.proposedNormal.x;
 				dy = knot.proposedNormal.y;
 			} else {
-				dx = normalX(knot.origTangent, this.contrast);
-				dy = normalY(knot.origTangent, this.contrast);
+				dx = normalX(knot.origTangent, this.m_contrast);
+				dy = normalY(knot.origTangent, this.m_contrast);
 			}
 			lhs[j].x = knot.x + knot.d1 * dx;
 			lhs[j].y = knot.y + knot.d1 * dy;
@@ -151,34 +79,34 @@ export class SpiroExpander {
 		const lhsUntransformed = [],
 			rhsUntransformed = [];
 		for (const z of lhs) {
-			const u = this.gizmo.unapply(z);
+			const u = this.m_gizmo.unapply(z);
 			lhsUntransformed.push({ type: z.type, x: u.x, y: u.y });
 		}
 		for (const z of rhs) {
-			const u = this.gizmo.unapply(z);
+			const u = this.m_gizmo.unapply(z);
 			rhsUntransformed.push({ type: z.type, x: u.x, y: u.y });
 		}
 		return { lhs, rhs, lhsUntransformed, rhsUntransformed };
 	}
 	interpolateUnimportantKnots(lhs, rhs) {
-		for (let j = 0; j < this.controlKnots.length; j++) {
-			const knot = this.controlKnots[j];
+		for (let j = 0; j < this.m_biKnots.length; j++) {
+			const knot = this.m_biKnots[j];
 			if (!knot.unimportant) continue;
 			let jBefore, jAfter;
-			for (jBefore = j - 1; cyNth(this.controlKnots, jBefore).unimportant; jBefore--);
-			for (jAfter = j + 1; cyNth(this.controlKnots, jAfter).unimportant; jAfter++);
-			const knotBefore = this.gizmo.unapply(cyNth(this.controlKnots, jBefore)),
-				knotAfter = this.gizmo.unapply(cyNth(this.controlKnots, jAfter)),
-				ref = this.gizmo.unapply(knot),
-				lhsBefore = this.gizmo.unapply(cyNth(lhs, jBefore)),
-				lhsAfter = this.gizmo.unapply(cyNth(lhs, jAfter)),
-				rhsBefore = this.gizmo.unapply(cyNth(rhs, jBefore)),
-				rhsAfter = this.gizmo.unapply(cyNth(rhs, jAfter));
-			const lhsTf = this.gizmo.applyXY(
+			for (jBefore = j - 1; cyNth(this.m_biKnots, jBefore).unimportant; jBefore--);
+			for (jAfter = j + 1; cyNth(this.m_biKnots, jAfter).unimportant; jAfter++);
+			const knotBefore = this.m_gizmo.unapply(cyNth(this.m_biKnots, jBefore)),
+				knotAfter = this.m_gizmo.unapply(cyNth(this.m_biKnots, jAfter)),
+				ref = this.m_gizmo.unapply(knot),
+				lhsBefore = this.m_gizmo.unapply(cyNth(lhs, jBefore)),
+				lhsAfter = this.m_gizmo.unapply(cyNth(lhs, jAfter)),
+				rhsBefore = this.m_gizmo.unapply(cyNth(rhs, jBefore)),
+				rhsAfter = this.m_gizmo.unapply(cyNth(rhs, jAfter));
+			const lhsTf = this.m_gizmo.applyXY(
 				linreg(knotBefore.x, lhsBefore.x, knotAfter.x, lhsAfter.x, ref.x),
 				linreg(knotBefore.y, lhsBefore.y, knotAfter.y, lhsAfter.y, ref.y)
 			);
-			const rhsTf = this.gizmo.applyXY(
+			const rhsTf = this.m_gizmo.applyXY(
 				linreg(knotBefore.x, rhsBefore.x, knotAfter.x, rhsAfter.x, ref.x),
 				linreg(knotBefore.y, rhsBefore.y, knotAfter.y, rhsAfter.y, ref.y)
 			);
@@ -189,33 +117,33 @@ export class SpiroExpander {
 }
 class NormalRectifier {
 	constructor(stage1ControlKnots, gizmo) {
-		this.gizmo = gizmo;
-		this.controlKnots = stage1ControlKnots;
-		this.nKnotsProcessed = 0;
+		this.m_gizmo = gizmo;
+		this.m_biKnots = stage1ControlKnots;
+		this.m_nKnotsProcessed = 0;
 	}
 	beginShape() {}
 	endShape() {}
 	moveTo(x, y) {
-		this.nKnotsProcessed += 1;
+		this.m_nKnotsProcessed += 1;
 	}
 	arcTo(arc, x, y) {
-		if (this.nKnotsProcessed === 1) {
-			const d = this.gizmo.applyOffsetXY(arc.deriveX0, arc.deriveY0);
+		if (this.m_nKnotsProcessed === 1) {
+			const d = this.m_gizmo.applyOffsetXY(arc.deriveX0, arc.deriveY0);
 			if (isTangentValid(d)) {
-				this.controlKnots[0].origTangent = d;
+				this.m_biKnots[0].origTangent = d;
 			} else {
 				throw new Error("NaN angle detected.");
 			}
 		}
-		if (this.controlKnots[this.nKnotsProcessed]) {
-			const d = this.gizmo.applyOffsetXY(arc.deriveX1, arc.deriveY1);
+		if (this.m_biKnots[this.m_nKnotsProcessed]) {
+			const d = this.m_gizmo.applyOffsetXY(arc.deriveX1, arc.deriveY1);
 			if (isTangentValid(d)) {
-				this.controlKnots[this.nKnotsProcessed].origTangent = d;
+				this.m_biKnots[this.m_nKnotsProcessed].origTangent = d;
 			} else {
 				throw new Error("NaN angle detected.");
 			}
 		}
-		this.nKnotsProcessed += 1;
+		this.m_nKnotsProcessed += 1;
 	}
 }