diff --git a/www/assert/main.js b/www/assert/main.js
index f8177a03f..657488b81 100644
--- a/www/assert/main.js
+++ b/www/assert/main.js
@@ -132,6 +132,40 @@ define([
         strungJSON(orig);
     });
 
+    HTML_list.forEach(function (sel) {
+        var el = $(sel)[0];
+
+        var pred = function (el) {
+            if (el.nodeName === 'DIV') {
+                return true;
+            }
+        };
+
+        var filter = function (x) {
+            console.log(x);
+            if (x[1]['class']) {
+                x[1]['class'] = x[1]['class'].replace(/cke/g, '');
+            }
+            return x;
+        };
+
+        assert(function (cb) {
+            // FlatDOM output
+            var map = Flat.fromDOM(el, pred, filter);
+
+            // Hyperjson output
+            var hj = Hyperjson.fromDOM(el, pred, filter);
+
+            var x = Flat.toDOM(map);
+            var y = Hyperjson.toDOM(hj);
+
+            console.error(x.outerHTML);
+            console.error(y.outerHTML);
+
+            cb(x.outerHTML === y.outerHTML);
+        }, "Test equality of FlatDOM and HyperJSON");
+    });
+
     // check that old hashes parse correctly
     assert(function (cb) {
         //if (1) { return cb(true); } // TODO(cjd): This is a test failure which is a known bug
diff --git a/www/common/flat-dom.js b/www/common/flat-dom.js
index 25b51d786..d54e9db55 100644
--- a/www/common/flat-dom.js
+++ b/www/common/flat-dom.js
@@ -17,8 +17,7 @@ define([], function () {
         return data;
     };
 
-    var identity = function (x) { return x; };
-    Flat.fromDOM = function (dom) {
+    Flat.fromDOM = function (dom, predicate, filter) {
         var data = {
             map: {},
         };
@@ -34,14 +33,21 @@ define([], function () {
                 return id;
             }
             if (!el || !el.attributes) { return; }
+            if (predicate) {
+                if (!predicate(el)) { return; } // shortcircuit
+            }
+
             id = uid();
-            data.map[id] = [
+            var temp = [
                 el.tagName,
                 getAttrs(el),
                 slice(el.childNodes).map(function (e) {
                     return process(e);
-                }).filter(identity)
+                }).filter(Boolean)
             ];
+
+            data.map[id] = filter? filter(temp): temp;
+
             return id;
         };