diff --git a/packages/minimongo/package.js b/packages/minimongo/package.js
index 6913f2af6c..d87d72dc29 100644
--- a/packages/minimongo/package.js
+++ b/packages/minimongo/package.js
@@ -8,7 +8,7 @@ Package.on_use(function (api, where) {
 
   // It would be sort of nice if minimongo didn't depend on
   // underscore, so we could ship it separately.
-  api.use(['underscore', 'json', 'ejson'], where);
+  api.use(['underscore', 'json', 'ejson', 'ordereddict'], where);
 
   api.add_files([
     'minimongo.js',
diff --git a/packages/ordereddict/ordereddict.js b/packages/ordereddict/ordereddict.js
new file mode 100644
index 0000000000..769e88672c
--- /dev/null
+++ b/packages/ordereddict/ordereddict.js
@@ -0,0 +1,158 @@
+(function () {
+  var element = function (key, value, next, prev) {
+    return {
+      key: key,
+      value: value,
+      next: next,
+      prev: prev
+    };
+  };
+  OrderedDict = function (/* ... */) {
+    var self = this;
+    self._dict = {};
+    self._first = null;
+    self._last = null;
+    _.each(arguments, function (kv) {
+      self.putBefore(kv[0], kv[1], null);
+    });
+  };
+
+  _.extend(OrderedDict.prototype, {
+    putBefore: function (key, item, before) {
+      var self = this;
+      var elt = before ?
+            element(key, item, self._dict[before]) :
+            element(key, item, null);
+      if (elt.next === undefined)
+        throw new Error("could not find item to put this one before");
+      if (!elt.next) {
+        elt.prev = self._last;
+        self._last.next = elt;
+        self._last = elt;
+      } else {
+        elt.prev = elt.next.prev;
+        elt.next.prev = elt;
+        elt.prev.next = elt;
+      }
+      if (self._first === null || self._first === elt.next)
+        self._first = elt;
+    },
+    remove: function (key) {
+      var self = this;
+      var elt = self._dict[key];
+      if (elt !== undefined) {
+        elt.next.prev = elt.prev;
+        elt.prev.next = elt.next;
+        if (elt === self._last)
+          self._last = elt.prev;
+        if (elt === self._first)
+          self._first = elt.next;
+        delete self._dict[key];
+        return elt.value;
+      } else {
+        return undefined;
+      }
+    },
+    get: function (key) {
+      var self = this;
+      if (_.has(self._dict, key))
+          return self._dict[key].value;
+      return undefined;
+    },
+    has: function (key) {
+      var self = this;
+      return _.has(self._dict[key]);
+    },
+    each: function (iter) {
+      var self = this;
+      var i = 0;
+      var elt = self._first;
+      while (elt !== null) {
+        var b = iter(elt.value, elt.key, i);
+        if (b === OrderedDict.BREAK)
+          return;
+        elt = elt.next;
+      }
+    },
+    first: function () {
+      var self = this;
+      return self._first.key;
+    },
+    firstValue: function () {
+      var self = this;
+      return self._first.value;
+    },
+    last: function () {
+      var self = this;
+      return self._last.key;
+    },
+    lastValue: function () {
+      var self = this;
+      return self._last.value;
+    },
+    prev: function (key) {
+      var self = this;
+      if (_.has(self._dict, key)) {
+        var elt = self._dict[key];
+        if (elt.prev)
+          return elt.prev.key;
+      }
+      return null;
+    },
+    next: function (key) {
+      var self = this;
+      if (_.has(self._dict, key)) {
+        var elt = self._dict[key];
+        if (elt.next)
+          return elt.next.key;
+      }
+      return null;
+    },
+    moveBefore: function (key, before) {
+      var self = this;
+      var elt = self._dict[key];
+      var eltBefore = before ? self._dict[before] : null;
+      if (elt === undefined)
+        throw new Error("Item to move is not present");
+      if (eltBefore === undefined)
+        throw new Error("Could not find element to move this one before");
+      if (eltBefore === elt.next) // no moving necessary.
+        return;
+      // remove from its old place
+      elt.next.prev = elt.prev;
+      elt.prev.next = elt.next;
+      if (elt === self._last)
+        self._last = elt.prev;
+      if (elt === self._first)
+        self._first = elt.next;
+
+      // now patch it in to its new place
+      if (eltBefore === null) {
+        elt.next = null;
+        elt.prev = self._last;
+        self._last.next = elt.prev;
+        self._last = elt;
+      } else {
+        elt.next = eltBefore;
+        elt.prev = eltBefore.prev;
+        eltBefore.prev = elt;
+        elt.prev.next = elt;
+      }
+
+    },
+    getIndex: function (key) {
+      var self = this;
+      var ret = null;
+      self.each(function (v, k, i) {
+        if (k === key) {
+          ret = i;
+          return OrderedDict.BREAK;
+        }
+        return undefined;
+      });
+      return ret;
+    }
+  });
+
+OrderedDict.BREAK = {break: true};
+})();
diff --git a/packages/ordereddict/package.js b/packages/ordereddict/package.js
new file mode 100644
index 0000000000..c248a27020
--- /dev/null
+++ b/packages/ordereddict/package.js
@@ -0,0 +1,9 @@
+Package.describe({
+  summary: "Ordered traversable dictionary with a mutable ordering",
+  internal: true
+});
+
+Package.on_use(function (api) {
+  api.use('underscore');
+  api.add_files('ordereddict.js', ['client', 'server']);
+});
diff --git a/packages/spark/spark.js b/packages/spark/spark.js
index 866c64db09..58756215cf 100644
--- a/packages/spark/spark.js
+++ b/packages/spark/spark.js
@@ -892,15 +892,18 @@ Spark.list = function (cursor, itemFunc, elseFunc) {
   });
 
   // Get the current contents of the cursor.
-  // XXX currently we count on observe() using only added() to deliver
-  // the initial contents. are we allow to do that, or do we need to
-  // implement removed/moved/changed here as well?
+
+  // TODO: unify initialContents and itemRanges into one
+  // OrderedDict from id -> (doc, LiveRange), called
+  // `itemDict`.
   var initialContents = [];
   _.extend(callbacks, {
     added: function (item, beforeIndex) {
+      // TODO: itemDict.addBefore ...
       initialContents.splice(beforeIndex, 0, item);
     }
   });
+  // TODO: observeChanges
   var handle = cursor.observe(observerCallbacks);
 
   // Get the renderer, if any
@@ -914,15 +917,18 @@ Spark.list = function (cursor, itemFunc, elseFunc) {
   // off for later.
   var html = '';
   var outerRange;
+  // TODO: itemRanges is a map from id to LiveRange
   var itemRanges = [];
   if (! initialContents.length)
     html = elseFunc();
   else {
+    // TODO: iterate over itemDict
     for (var i = 0; i < initialContents.length; i++) {
       (function (i) {
         html += maybeAnnotate(itemFunc(initialContents[i]),
                               Spark._ANNOTATION_LIST_ITEM,
                               function (range) {
+                                // TOOD: mutate value in itemDict
                                 itemRanges[i] = range;
                               });
       })(i); // scope i to closure