diff --git a/artworld/drawable.js b/artworld/drawable.js
index e280c92..05045dd 100644
--- a/artworld/drawable.js
+++ b/artworld/drawable.js
@@ -1,4 +1,3 @@
-import { artworld } from "./world.js";
 import { Vector2 } from "./math.js";
 import { Color } from "./color.js";
 import { Random } from "./random.js";
@@ -10,13 +9,12 @@ export class Drawable {
     this._fill = parent ? parent._fill : null;
     this._stroke = parent ? parent._stroke : null;
     this._strokeWeight = parent ? parent._strokeWeight : null;
-    this._z_index = parent ? parent._z_index : null;
+    this._zIndex = parent ? parent._zIndex : null;
     this._posVec = new Vector2(0, 0);
     this._animations = [];
     if (this._parent) {
       this._parent.addChild(this);
     }
-    artworld.register(this);
   }
 
   copy() {
@@ -71,7 +69,7 @@ export class Drawable {
   }
 
   z(scalar) {
-    this._z_index = scalar;
+    this._zIndex = scalar;
     return this;
   }
 
@@ -83,10 +81,7 @@ export class Drawable {
   }
 
   random() {
-    this._posVec = new Vector2(
-      Random.under(artworld.width),
-      Random.under(artworld.height),
-    );
+    this._posVec = new Vector2(Random.under(100), Random.under(100));
     this._stroke = new Color(
       Random.under(360),
       Random.between(30, 60),
@@ -137,11 +132,16 @@ export class Group extends Drawable {
     return newGroup;
   }
 
-  draw() {}
+  draw() {
+    for (let c of this._children) {
+      c.draw();
+    }
+  }
 
   addChild(drawable) {
     this._children.push(drawable);
     drawable._parent = this;
+    drawable._world = this._world;
     return this;
   }
 
diff --git a/artworld/index.js b/artworld/index.js
index cebaaef..d8d16cc 100644
--- a/artworld/index.js
+++ b/artworld/index.js
@@ -1,7 +1,7 @@
-export { artworld } from "./world.js";
 export { Color, Pico8 } from "./color.js";
 export { Vector2, degToRad, radToDeg } from "./math.js";
 export { Line, Rect, Circle, Arc, Polygon } from "./shapes.js";
 export { Group } from "./drawable.js";
 export { Random } from "./random.js";
 export { Var } from "./variables.js";
+export { World } from "./world.js";
diff --git a/artworld/shapes.js b/artworld/shapes.js
index 1f4ef0e..b979860 100644
--- a/artworld/shapes.js
+++ b/artworld/shapes.js
@@ -32,8 +32,8 @@ export class Line extends Drawable {
   }
 
   draw() {
-    artworld.prepareDraw(this);
-    artworld.drawLine(
+    this._world.prepareDraw(this);
+    this._world.drawLine(
       this.worldPos,
       this.worldPos.add(getVal(this._offsetVec)),
     );
@@ -70,8 +70,13 @@ export class Arc extends Drawable {
     return this;
   }
   draw() {
-    artworld.prepareDraw(this);
-    artworld.drawArc(this.worldPos, this._r, this._startAngle, this._endAngle);
+    this._world.prepareDraw(this);
+    this._world.drawArc(
+      this.worldPos,
+      this._r,
+      this._startAngle,
+      this._endAngle,
+    );
   }
 
   radius(scalar) {
@@ -104,8 +109,8 @@ export class Circle extends Drawable {
   }
 
   draw() {
-    artworld.prepareDraw(this);
-    artworld.drawArc(this.worldPos, this._r, 0, 2 * Math.PI);
+    this._world.prepareDraw(this);
+    this._world.drawArc(this.worldPos, this._r, 0, 2 * Math.PI);
   }
 
   radius(scalar) {
@@ -132,8 +137,8 @@ export class Rect extends Drawable {
   }
 
   draw() {
-    artworld.prepareDraw(this);
-    artworld.drawRect(this.worldPos, this._width, this._height);
+    this._world.prepareDraw(this);
+    this._world.drawRect(this.worldPos, this._width, this._height);
   }
 
   size(w, h) {
@@ -204,8 +209,8 @@ export class Polygon extends Drawable {
   }
 
   draw() {
-    artworld.prepareDraw(this);
-    artworld.drawPolygon(this.worldPos, this._points);
+    this._world.prepareDraw(this);
+    this._world.drawPolygon(this.worldPos, this._points);
   }
 
   point(vector, to_modify = null) {
diff --git a/artworld/variables.js b/artworld/variables.js
index dbe5a44..ccffe4b 100644
--- a/artworld/variables.js
+++ b/artworld/variables.js
@@ -1,5 +1,3 @@
-import { artworld } from "./world.js";
-
 export function getVal(x) {
   return x && x.getValue ? x.getValue() : x;
 }
@@ -13,7 +11,6 @@ export class Var {
       this._value = value;
       this._updateFunc = null;
     }
-    artworld.register(this);
   }
 
   updateFunc(func) {
diff --git a/artworld/world.js b/artworld/world.js
index cdc978c..aa29a73 100644
--- a/artworld/world.js
+++ b/artworld/world.js
@@ -2,7 +2,7 @@ import { Timer } from "./timer.js";
 import { getVal, Var } from "./variables.js";
 
 export class World {
-  constructor() {
+  constructor(canvasId) {
     this.ctx = null;
     this.drawables = [];
     this.variables = [];
@@ -12,10 +12,7 @@ export class World {
     this.stepSize = 1000 / this.targetFrameRate;
     this.lastTick = this.timer.time();
     this.numTicks = 0;
-  }
-
-  bindCanvas(id) {
-    this.ctx = document.getElementById(id).getContext("2d");
+    this.ctx = document.getElementById(canvasId).getContext("2d");
   }
 
   get width() {
@@ -26,22 +23,24 @@ export class World {
     return this.ctx.canvas.height;
   }
 
-  // TODO rename
-  register(thing) {
-    if (thing instanceof Var) {
-      this.variables.push(thing);
-    } else {
-      // TODO: check drawable?
-      this.drawables.push(thing);
-    }
+  var(value) {
+    let v = new Var(value);
+    this.variables.push(v);
+    return v;
+  }
+
+  drawable(thing) {
+    this.drawables.push(thing);
+    thing._world = this; // set world for access to renderer (TODO: revisit)
+    return thing;
   }
 
   draw() {
-    this.ctx.fillStyle = "white";
+    this.ctx.fillStyle = this.backgroundColor;
     this.ctx.beginPath();
     this.ctx.fillRect(0, 0, this.width, this.height);
     this.ctx.fill();
-    for (let d of this.drawables.sort((a, b) => a._z_index - b._z_index)) {
+    for (let d of this.drawables.sort((a, b) => a._zIndex - b._zIndex)) {
       d.draw();
     }
   }
@@ -134,6 +133,3 @@ export class World {
     if (this._fill) this.ctx.fill();
   }
 }
-
-// singleton (for now)
-export const artworld = new World();
diff --git a/examples/dataclock.html b/examples/dataclock.html
index ac0d20d..5ddd9e7 100644
--- a/examples/dataclock.html
+++ b/examples/dataclock.html
@@ -4,7 +4,7 @@
     <canvas id="mainCanvas" width="500" height="500"></canvas>
     <script type="module">
       import {
-        artworld,
+        World,
         Color,
         Pico8,
         Group,
@@ -16,32 +16,42 @@
         Var,
         degToRad,
       } from "../artworld/index.js";
-      artworld.bindCanvas("mainCanvas");
-      window.artworld = artworld;
 
-      // declare some time-fluctuation variables
-      let color = new Var(
+      let world = new World("mainCanvas");
+      window.world = world;
+      // This is an experiment to separate the declaration of
+      // "what the data does" from "what it looks like".
+
+      // First we use `Var` to define "what the data does"
+      //  variables are expected to regularly *vary*!
+
+      // Variables are defined as functions that update with time.
+      // It is also possible to define static variables.
+      let color = world.var(
         (t) =>
           [Pico8.RED, Pico8.ORANGE, Pico8.GREEN, Pico8.BLUE][
             Math.floor(t / 60) % 4
           ],
       );
-      let outerR = new Var((t) => Math.sin(t / 100) * 50 + 200);
-      // simple dependency
-      let innerR = new Var(() => outerR.getValue() - 10);
-      // example of a more complex Var that uses other vars
-      let lineTo = new Var((t) => {
+      // We can create dependencies between them: here the inner & outer
+      // radii should be 10 pixels apart.
+      let outerR = world.var((t) => Math.sin(t / 100) * 50 + 200);
+      let innerR = world.var(() => outerR.getValue() - 10);
+      // We take this composition a bit further here, the radius of the clock
+      // hand grows & shrinks with the edge.
+      let lineTo = world.var((t) => {
         let angle = (t / 6000) * Math.PI * 2;
         return Vector2.polar(innerR.getValue(), angle);
       });
 
       let g = new Group().pos(new Vector2(250, 250));
+      world.drawable(g);
       new Circle(g).fill(Pico8.BLACK).z(1).radius(outerR);
       new Circle(g).z(10).fill(color).radius(innerR);
       new Circle(g).radius(20).fill(Pico8.BLACK).z(50);
       new Line(g).to(lineTo).z(100);
 
-      artworld.loopStep();
+      world.loopStep();
     </script>
   </body>
 </html>