diff --git a/www/slide/slide.js b/www/slide/slide.js
index 0f5501c85..098cad315 100644
--- a/www/slide/slide.js
+++ b/www/slide/slide.js
@@ -1,8 +1,10 @@
 define([
     '/bower_components/marked/marked.min.js',
+    '/bower_components/diff-dom/diffDOM.js',
     '/bower_components/jquery/dist/jquery.min.js',
 ],function (Marked) {
     var $ = window.jQuery;
+    var DiffDOM = window.diffDOM;
 
     var truthy = function (x) { return x; };
 
@@ -17,13 +19,78 @@ define([
         $modal = Slide.$modal = $m;
         $content = Slide.$content = $c;
     };
+
+    var forbiddenTags = Slide.forbiddenTags = [
+        'SCRIPT',
+        'IFRAME',
+        'OBJECT',
+        'APPLET',
+        'VIDEO',
+        'AUDIO',
+    ];
+    var unsafeTag = function (info) {
+        if (['addAttribute', 'modifyAttribute'].indexOf(info.diff.action) !== -1) {
+            if (/^on/.test(info.diff.name)) {
+                console.log("Rejecting forbidden element attribute with name", info.diff.element.nodeName);
+                return true;
+            }
+        }
+        if (['addElement', 'replaceElement'].indexOf(info.diff.action) !== -1) {
+            var msg = "Rejecting forbidden tag of type (%s)";
+            if (info.diff.element && forbiddenTags.indexOf(info.diff.element.nodeName) !== -1) {
+                console.log(msg, info.diff.element.nodeName);
+                return true;
+            } else if (info.diff.newValue && forbiddenTags.indexOf(info.diff.newValue.nodeName) !== -1) {
+                console.log("Replacing restricted element type (%s) with PRE", info.diff.newValue.nodeName);
+                info.diff.newValue.nodeName = 'PRE';
+            }
+        }
+    };
+
+    var domFromHTML = Slide.domFromHTML = function (html) {
+        return new DOMParser().parseFromString(html, "text/html");
+    };
+
+    var DD = new DiffDOM({
+        preDiffApply: function (info) {
+            if (unsafeTag(info)) { return true; }
+        }
+    });
+
+    var makeDiff = function (A, B) {
+        var Err;
+        var Els = [A, B].map(function (frag) {
+            if (typeof(frag) === 'object') {
+                if (!frag && frag.body) {
+                    Err = "No body";
+                    return;
+                }
+                var els = frag.body.querySelectorAll('#content');
+                if (els.length) {
+                    return els[0];
+                }
+            }
+            Err = 'No candidate found';
+        });
+        if (Err) { return Err; }
+        var patch = DD.diff(Els[0], Els[1]);
+        return patch;
+    };
+
     var draw = Slide.draw =  function (i) {
         console.log("Trying to draw slide #%s", i);
         if (typeof(Slide.content[i]) !== 'string') { return; }
 
         var c = Slide.content[i];
-        console.log(c);
-        $content.html(Marked(c));
+        var Dom = domFromHTML('<div id="content">' + Marked(c) + '</div>');
+        var patch = makeDiff(domFromHTML($content[0].outerHTML), Dom);
+
+        if (typeof(patch) === 'string') {
+            $content.html(Marked(c));
+            return;
+        } else {
+            DD.apply($content[0], patch);
+        }
     };
 
     var show = Slide.show = function (bool, content) {
@@ -39,9 +106,11 @@ define([
 
     var update = Slide.update = function (content) {
         if (!Slide.shown) { return; }
-        console.log(content);
+        var old = Slide.content[Slide.index];
         Slide.content = content.split(/\n\s*\-\-\-\s*\n/).filter(truthy);
-        draw(Slide.index);
+        if (old !== Slide.content[Slide.index]) {
+            draw(Slide.index);
+        }
     };
 
     var left = Slide.left = function () {