diff --git a/core/block.js b/core/block.js
index 0e92d660a..16c8604a3 100644
--- a/core/block.js
+++ b/core/block.js
@@ -511,6 +511,7 @@ Blockly.Block.prototype.setShadow = function(shadow) {
   }
   this.isShadow_ = shadow;
   if (Blockly.Events.isEnabled() && !shadow) {
+    Blockly.Events.group = Blockly.genUid();
     // Fire a creation event.
     var xmlBlock = Blockly.Xml.blockToDom(this);
     Blockly.Events.fire(new Blockly.Events.Create(this.workspace, xmlBlock));
@@ -521,6 +522,7 @@ Blockly.Block.prototype.setShadow = function(shadow) {
     moveEvent.oldCoordinate = new goog.math.Coordinate(0, 0);
     moveEvent.recordNew();
     Blockly.Events.fire(moveEvent);
+    Blockly.Events.group = '';
   }
 };
 
diff --git a/core/block_svg.js b/core/block_svg.js
index aab5cffa0..70db3bbbe 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -460,6 +460,7 @@ Blockly.BlockSvg.prototype.onMouseDown_ = function(e) {
     // dragged instead.
     return;
   } else {
+    Blockly.Events.group = Blockly.genUid();
     // Left-click (or middle click)
     Blockly.removeAllRanges();
     Blockly.Css.setCursor(Blockly.Css.Cursor.CLOSED);
@@ -528,6 +529,7 @@ Blockly.BlockSvg.prototype.onMouseUp_ = function(e) {
     Blockly.highlightedConnection_ = null;
   }
   Blockly.Css.setCursor(Blockly.Css.Cursor.OPEN);
+  Blockly.Events.group = '';
 };
 
 /**
diff --git a/core/events.js b/core/events.js
index ddef12665..222737f1c 100644
--- a/core/events.js
+++ b/core/events.js
@@ -27,6 +27,12 @@
 goog.provide('Blockly.Events');
 
 
+/**
+ * Group ID for new events.  Grouped events are indivisible.
+ * @type {string}
+ */
+Blockly.Events.group = '';
+
 /**
  * Allow change events to be created and fired.
  * @type {number}
@@ -159,10 +165,14 @@ Blockly.Events.isEnabled = function() {
 };
 
 /**
- * Abstract class for a change event.
+ * Abstract class for an event.
+ * @param {!Blockly.Workspace} workspace The workspace.
  * @constructor
  */
-Blockly.Events.Abstract = function() {};
+Blockly.Events.Abstract = function(workspace) {
+  this.workspaceId = workspace.id;
+  this.group = Blockly.Events.group;
+};
 
 /**
  * Does this event record any change of state?
@@ -180,12 +190,17 @@ Blockly.Events.Abstract.prototype.isNull = function() {
  * @constructor
  */
 Blockly.Events.Create = function(workspace, xml) {
-  this.type = Blockly.Events.CREATE;
-  this.workspaceId = workspace.id;
+  Blockly.Events.Create.superClass_.constructor.call(this, workspace);
   this.xml = xml;
 };
 goog.inherits(Blockly.Events.Create, Blockly.Events.Abstract);
 
+/**
+ * Type of this event.
+ * @type {string}
+ */
+Blockly.Events.Create.prototype.type = Blockly.Events.CREATE;
+
 /**
  * Class for a block deletion event.
  * @param {!Blockly.Block} block The deleted block.
@@ -196,13 +211,18 @@ Blockly.Events.Delete = function(block) {
   if (block.getParent()) {
     throw 'Connected blocks cannot be deleted.';
   }
-  this.type = Blockly.Events.DELETE;
-  this.workspaceId = block.workspace.id;
+  Blockly.Events.Delete.superClass_.constructor.call(this, block.workspace);
   this.blockId = block.id;
   this.oldXml = Blockly.Xml.blockToDomWithXY(block);
 };
 goog.inherits(Blockly.Events.Delete, Blockly.Events.Abstract);
 
+/**
+ * Type of this event.
+ * @type {string}
+ */
+Blockly.Events.Delete.prototype.type = Blockly.Events.DELETE;
+
 /**
  * Class for a block change event.
  * @param {!Blockly.Block} block The deleted block.
@@ -214,15 +234,20 @@ goog.inherits(Blockly.Events.Delete, Blockly.Events.Abstract);
  * @constructor
  */
 Blockly.Events.Change = function(block, element, name, oldValue, newValue) {
-  this.type = Blockly.Events.CHANGE;
-  this.workspaceId = block.workspace.id;
+  Blockly.Events.Change.superClass_.constructor.call(this, block.workspace);
   this.blockId = block.id;
   this.element = element;
   this.name = name;
   this.oldValue = oldValue;
   this.newValue = newValue;
 };
-goog.inherits(Blockly.Events.Create, Blockly.Events.Abstract);
+goog.inherits(Blockly.Events.Change, Blockly.Events.Abstract);
+
+/**
+ * Type of this event.
+ * @type {string}
+ */
+Blockly.Events.Change.prototype.type = Blockly.Events.CHANGE;
 
 /**
  * Does this event record any change of state?
@@ -239,8 +264,7 @@ Blockly.Events.Change.prototype.isNull = function() {
  * @constructor
  */
 Blockly.Events.Move = function(block) {
-  this.type = Blockly.Events.MOVE;
-  this.workspaceId = block.workspace.id;
+  Blockly.Events.Move.superClass_.constructor.call(this, block.workspace);
   this.blockId = block.id;
 
   var location = this.currentLocation_();
@@ -250,6 +274,12 @@ Blockly.Events.Move = function(block) {
 };
 goog.inherits(Blockly.Events.Move, Blockly.Events.Abstract);
 
+/**
+ * Type of this event.
+ * @type {string}
+ */
+Blockly.Events.Move.prototype.type = Blockly.Events.MOVE;
+
 /**
  * Record the block's new location.  Called after the move.
  */
diff --git a/tests/playground.html b/tests/playground.html
index d8fadd60e..2f3d98167 100644
--- a/tests/playground.html
+++ b/tests/playground.html
@@ -81,6 +81,15 @@ function start() {
               scaleSpeed: 1.1
              },
           });
+  // Restore previously displayed text.
+  var text = sessionStorage.getItem('textarea');
+  if (text) {
+    document.getElementById('importExport').value = text;
+  }
+  taChange();
+  // Restore event logging state.
+  var state = sessionStorage.getItem('logEvents');
+  logEvents(Boolean(state));
 }
 
 function toXml() {
@@ -89,17 +98,49 @@ function toXml() {
   output.value = Blockly.Xml.domToPrettyText(xml);
   output.focus();
   output.select();
+  taChange();
 }
 
 function fromXml() {
   var input = document.getElementById('importExport');
   var xml = Blockly.Xml.textToDom(input.value);
   Blockly.Xml.domToWorkspace(workspace, xml);
+  taChange();
 }
 
 function toCode(lang) {
   var output = document.getElementById('importExport');
   output.value = Blockly[lang].workspaceToCode(workspace);
+  taChange();
+}
+
+// Disable the "Import from XML" button if the XML is invalid.
+// Preserve text between page reloads.
+function taChange() {
+  var textarea = document.getElementById('importExport');
+  sessionStorage.setItem('textarea', textarea.value)
+  var valid = true;
+  try {
+    Blockly.Xml.textToDom(textarea.value);
+  } catch (e) {
+    valid = false;
+  }
+  document.getElementById('import').disabled = !valid;
+}
+
+function logEvents(state) {
+  var checkbox = document.getElementById('logCheck');
+  checkbox.checked = state;
+  sessionStorage.setItem('logEvents', Number(state));
+  if (state) {
+    workspace.addChangeListener(logger);
+  } else {
+    workspace.removeChangeListener(logger);
+  }
+}
+
+function logger(e) {
+  console.log(e);
 }
 
 function airstrike(n) {
@@ -526,7 +567,7 @@ h1 {
   <p>
     <input type="button" value="Export to XML" onclick="toXml()">
     &nbsp;
-    <input type="button" value="Import from XML" onclick="fromXml()">
+    <input type="button" value="Import from XML" onclick="fromXml()" id="import">
     <br>
     <input type="button" value="To JavaScript" onclick="toCode('JavaScript')">
     &nbsp;
@@ -536,15 +577,19 @@ h1 {
     &nbsp;
     <input type="button" value="To Dart" onclick="toCode('Dart')">
     <br>
-    <textarea id="importExport" style="width: 26%; height: 12em"></textarea>
+    <textarea id="importExport" style="width: 26%; height: 12em"
+      onchange="taChange();" onkeyup="taChange()"></textarea>
   </p>
-  <hr>
 
   <p>
-    Stress test:
+    Stress test: &nbsp;
     <input type="button" value="Airstrike!" onclick="airstrike(100)">
     <input type="button" value="Spaghetti!" onclick="spaghetti(8)">
   </p>
+  <p>
+    Log events: &nbsp;
+    <input type="checkbox" onclick="logEvents(this.checked)" id="logCheck">
+  </p>
 
 </body>
 </html>