diff --git a/doc/jsdoc-conf.json b/doc/jsdoc-conf.json
new file mode 100644
index 00000000..d3120efe
--- /dev/null
+++ b/doc/jsdoc-conf.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["plugins/markdown", "jsdoc-plugin-jsio"]
+}
diff --git a/doc/jsdoc-plugin-jsio.js b/doc/jsdoc-plugin-jsio.js
new file mode 100644
index 00000000..b17cf35b
--- /dev/null
+++ b/doc/jsdoc-plugin-jsio.js
@@ -0,0 +1,71 @@
+// based on:
+//   https://github.com/gameclosure/eslint-plugin-jsio/blob/master/lib/index.js
+
+"use strict";
+
+exports.handlers = {
+    beforeParse: function(e) {
+        e.source = e.source.replace(importExpr, rewriteImports);
+    }
+};
+
+var importExpr = /^(\s*)(import\s+[^=+*"'\r\n;\/]+|from\s+[^=+"'\r\n;\/ ]+\s+import\s+[^=+"'\r\n;\/]+)(;|\/|$)/gm;
+
+function rewriteImports(raw, p1, p2, p3) {
+  if (!/\/\//.test(p1)) {
+    var declarations = getDeclarations(p2);
+    var vars = declarations.vars;
+    var requireStatements = declarations.requireStatements;
+    return p1
+      + ((vars.length ? 'var ' + vars.map(function (declaration) {
+        return declaration.replace(/^\.+/, '').split('.')[0];
+      }).join(',') + ';' : '')
+      + (requireStatements.length ? requireStatements.map(function (statement) {
+        return 'require(\'' + statement + '\');';
+      }).join('') : '')).replace(/;$/, '')
+      + p3;
+  }
+
+  return raw;
+}
+
+function getDeclarations(importStatement) {
+  var vars = [];
+  var requireStatements = [];
+  // from myPackage import myFunc
+  // external myPackage import myFunc
+  var match = importStatement.match(/^\s*(from|external)\s+([\w.\-$]+)\s+(import|grab)\s+(.*)$/);
+  if (match) {
+    requireStatements.push(requireify(match[2]));
+    match[4].replace(/\s*([\w.\-$*]+)(?:\s+as\s+([\w.\-$]+))?/g, function(_, item, as) {
+      vars.push(as || item);
+    });
+  }
+
+  if (!match) {
+    match = importStatement.match(/^\s*import\s+(.*)$/);
+    if (match) {
+      match[1].replace(/\s*([\w.\-$]+)(?:\s+as\s+([\w.\-$]+))?,?/g, function(_, fullPath, as) {
+        requireStatements.push(requireify(fullPath));
+        vars.push(as || fullPath);
+      });
+    }
+  }
+
+  return {
+    requireStatements: requireStatements,
+    vars: vars
+  };
+}
+
+function requireify(path) {
+  var match = path.match(/^(\.*)(.*)$/);
+  var leadingDots = match[1];
+  var remainder = match[2];
+  return (leadingDots.length == 1
+            ? './'
+            : leadingDots.length > 1
+              ? leadingDots.substring(1).split('.').join('../')
+              : '')
+        + remainder.replace(/\./g, '/');
+}
diff --git a/src/timer.js b/src/timer.js
index d74c423b..6869f2a5 100644
--- a/src/timer.js
+++ b/src/timer.js
@@ -15,68 +15,144 @@
  */
 
 /**
- * @module timer
+ * Provides an interface to the time for a timestep app.  The interface can be
+ * queried by the app for information about elapsed time.  It is consumed by the
+ * timestep {@link Engine} to drive the Engine's tick and render.
+ *
+ * Use {@linkcode module:timer.maxTick|maxTick} and {@linkcode
+ * module:timer.tickCap|tickCap} to control the behavior of the timer.
+ *
+ * For example, assume `maxTick = 100000` (10,000ms) and `tickCap = 100`
+ * (100ms).  The following behavior will occur for various tick `dt` values:
+ *  - `20 ⟶ onTick(20)`
+ *  - `100 ⟶ onTick(100)`
+ *  - `120 ⟶ onTick(100)`
+ *  - `9999 ⟶ onTick(100)`
+ *  - `10000 ⟶ onTick(10000)`
+ *  - `10001 ⟶ onLargeTick(10001, 10000); onTick(1)`
+ *  - `40000 ⟶ onLargeTick(40000, 10000); onTick(1)`
  *
- * Implements an independent, singleton timer for use by the environment.
- * The Application Engine binds to this to generate the rendering tick.
+ * @module timer
  */
 
 import device;
 
 var Timer = device.get('Timer');
 
-var MAX_TICK = 10000; // ticks over 10 seconds will be considered too large to process
-exports.now = 0;
-exports.frames = 0;
-exports.reset = function () { this._last = null; }
-exports.tick = function (dt) {
-  try {
-    if (dt > MAX_TICK) {
-      exports.onLargeTick(dt, MAX_TICK);
-      dt = 1;
-    }
-    
-    exports.now += dt;
-    exports.frames++;
-    exports.onTick(dt);
-    ok = true;
-  } finally {
-    if (exports.debug && !ok) {
-      app.stopLoop()
-    }
-  }
-}
+// ticks over 10 seconds will be considered too large to forward to the app
+var _maxTick = 10 * 1000;
+var _tickCap = _maxTick;
+var _now = 0;
+var _frames = 0;
 
 /**
- * If our computer falls asleep, dt might be an insanely large number. 
- * If we're running a simulation of sorts, we don't want the computer
- * to freeze while computing 1000s of simulation steps, so just drop
- * this tick.  Anyone who is interested can listen for a call to 'onLargeTick'
+ * Defines the maximum milliseconds for a tick before the tick is dropped and
+ * {@linkcode module:timer.onLargeTick|onLargeTick} is called. {@linkcode
+ * module:timer.onTick|onTick} will also be called with a `dt` of 1.
+ * @member module:timer.maxTick {integer}
+ * @default 10,000
  */
-exports.onLargeTick = function (largeDt, threshold) {
-  logger.warn('Dropping large tick: ' + largeDt + '; Threshold is set at: ' + threshold);
-}
+Object.defineProperty(exports, 'maxTick', {
+  get: function () { return _maxTick; },
+  set: function (value) { _maxTick = value; }
+});
+
+/**
+ * Defines the maximum value of `dt`.  If a tick `dt` is above the cap,
+ * {@linkcode module:timer.onTick|onTick} is called with `tickCap` rather than
+ * `dt`.
+ * @member module:timer.tickCap {integer}
+ * @default 10,000
+ */
+exports.tickCap;
+Object.defineProperty(exports, 'tickCap', {
+  get: function () { return _tickCap; },
+  set: function (value) { _tickCap = value; }
+});
 
-exports.onTick = function (dt) {}
+/**
+ * number of milliseconds since timer started
+ * @member module:timer.now {integer}
+ * @readonly
+ */
+Object.defineProperty(exports, 'now', {
+  get: function () { return _now; }
+});
 
-exports.debug = false;
+/**
+ * number of frames since timer started
+ * @member module:timer.frames {integer}
+ * @readonly
+ */
+Object.defineProperty(exports, 'frames', {
+  get: function () { return _frames; }
+});
 
+/**
+ * resets the timer's properties `now` and `frames` (sets them to 0)
+ */
+exports.reset = function () {
+  _now = 0;
+  _frames = 0;
+};
 
-// TODO: <jsio>('from iOS import start as exports.start, stop as exports.stop');
+exports.tick = function (dt) {
+  if (dt > _maxTick) {
+    exports.onLargeTick(dt, _maxTick);
+    dt = 1;
+  }
 
+  if (dt > _tickCap) {
+    dt = _tickCap;
+  }
+
+  _now += dt;
+  _frames++;
+
+  exports.onTick(dt);
+};
+
+/**
+ * Starts/resumes the timer
+ */
 exports.start = function (minDt) {
-  this.reset();
-  this.isRunning = true;
+  exports.isRunning = true;
   device.get('Timer').start(exports.tick, minDt);
-}
+};
 
+/**
+ * Stops/pauses the timer
+ */
 exports.stop = function () {
-  this.reset();
-  this.isRunning = false;
+  exports.isRunning = false;
   device.get('Timer').stop();
-}
+};
 
+/**
+ * Computes and returns the number of milliseconds into the current frame
+ * execution has progressed since the last tick (and before the next one)
+ */
 exports.getTickProgress = function () {
-  var now = +new Date;
-  return (-(Timer.last || now) + now);
-}
+  var now = Date.now();
+  return now - (Timer.last || now);
+};
+
+/**
+ * Override this function to capture large ticks.  Large ticks may happen if the
+ * app is backgrounded or paused.  The default behavior is to log a warning with
+ * the value of the dropped tick.
+ * @param largeDt {integer} number of milliseconds in the large tick
+ * @param threshold {integer} current value of {@linkcode
+ *     module:timer.maxTick|maxTick}
+ */
+exports.onLargeTick = function (largeDt, threshold) {
+  logger.warn('Dropping large tick: ' + largeDt + '; Threshold is set at: '
+      + threshold);
+};
+
+/**
+ * Used internally by the timestep {@link Engine} for driving `tick` and
+ * `render`.
+ * @param _dt {integer} milliseconds since last tick
+ */
+exports.onTick = function (_dt) {};