diff --git a/core/block_svg.js b/core/block_svg.js
index 4ea6f288d..f7727980c 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -127,6 +127,7 @@ Blockly.BlockSvg.prototype.select = function() {
     // Unselect any previously selected block.
     Blockly.selected.unselect();
   }
+  Blockly.Events.fire(new Blockly.Events.Ui(this, 'selected', false, true));
   Blockly.selected = this;
   this.addSelect();
   Blockly.fireUiEvent(this.workspace.getCanvas(), 'blocklySelectChange');
@@ -136,6 +137,10 @@ Blockly.BlockSvg.prototype.select = function() {
  * Unselect this block.  Remove its highlighting.
  */
 Blockly.BlockSvg.prototype.unselect = function() {
+  if (Blockly.selected != this) {
+    return;
+  }
+  Blockly.Events.fire(new Blockly.Events.Ui(this, 'selected', true, false));
   Blockly.selected = null;
   this.removeSelect();
   Blockly.fireUiEvent(this.workspace.getCanvas(), 'blocklySelectChange');
diff --git a/core/comment.js b/core/comment.js
index fd7816ac5..06c9bae77 100644
--- a/core/comment.js
+++ b/core/comment.js
@@ -164,6 +164,8 @@ Blockly.Comment.prototype.setVisible = function(visible) {
     // No change.
     return;
   }
+  Blockly.Events.fire(
+      new Blockly.Events.Ui(this.block_, 'commentOpen', !visible, visible));
   if ((!this.block_.isEditable() && !this.textarea_) || goog.userAgent.IE) {
     // Steal the code from warnings to make an uneditable text bubble.
     // MSIE does not support foreignobject; textareas are impossible.
diff --git a/core/events.js b/core/events.js
index d532a6a5f..417d59470 100644
--- a/core/events.js
+++ b/core/events.js
@@ -71,6 +71,12 @@ Blockly.Events.CHANGE = 'change';
  */
 Blockly.Events.MOVE = 'move';
 
+/**
+ * Name of event that records a UI change.
+ * @const
+ */
+Blockly.Events.UI = 'ui';
+
 /**
  * List of events queued for firing.
  * @private
@@ -254,6 +260,14 @@ Blockly.Events.Abstract.prototype.isNull = function() {
   return false;
 };
 
+/**
+ * Run an event.
+ * @param {boolean} forward True if run forward, false if run backward (undo).
+ */
+Blockly.Events.Abstract.prototype.run = function(forward) {
+  // Defined by subclasses.
+};
+
 /**
  * Class for a block creation event.
  * @param {!Blockly.Block} block The created block.
@@ -572,3 +586,47 @@ Blockly.Events.Move.prototype.run = function(forward) {
     }
   }
 };
+
+/**
+ * Class for a UI event.
+ * @param {!Blockly.Block} block The affected block.
+ * @param {string} element One of 'selected', 'comment', 'mutator', etc.
+ * @param {string} oldValue Previous value of element.
+ * @param {string} newValue New value of element.
+ * @extends {Blockly.Events.Abstract}
+ * @constructor
+ */
+Blockly.Events.Ui = function(block, element, oldValue, newValue) {
+  Blockly.Events.Ui.superClass_.constructor.call(this, block);
+  this.element = element;
+  this.oldValue = oldValue;
+  this.newValue = newValue;
+  this.recordUndo = false;
+};
+goog.inherits(Blockly.Events.Ui, Blockly.Events.Abstract);
+
+/**
+ * Type of this event.
+ * @type {string}
+ */
+Blockly.Events.Ui.prototype.type = Blockly.Events.UI;
+
+/**
+ * Encode the event as JSON.
+ * @return {!Object} JSON representation.
+ */
+Blockly.Events.Change.prototype.toJson = function() {
+  var json = Blockly.Events.Change.superClass_.toJson.call(this);
+  json['element'] = this.element;
+  json['newValue'] = this.newValue;
+  return json;
+};
+
+/**
+ * Does this event record any change of state?
+ * @return {boolean} True if something changed.
+ */
+Blockly.Events.Ui.prototype.isNull = function() {
+  return this.oldValue == this.newValue;
+};
+
diff --git a/core/mutator.js b/core/mutator.js
index eb488e833..e8cfac42c 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -198,6 +198,8 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
     // No change.
     return;
   }
+  Blockly.Events.fire(
+      new Blockly.Events.Ui(this.block_, 'mutatorOpen', !visible, visible));
   if (visible) {
     // Create the bubble.
     this.bubble_ = new Blockly.Bubble(this.block_.workspace,
diff --git a/core/warning.js b/core/warning.js
index 8d990b1d2..4ec8bf771 100644
--- a/core/warning.js
+++ b/core/warning.js
@@ -105,6 +105,8 @@ Blockly.Warning.prototype.setVisible = function(visible) {
     // No change.
     return;
   }
+  Blockly.Events.fire(
+      new Blockly.Events.Ui(this.block_, 'warningOpen', !visible, visible));
   if (visible) {
     // Create the bubble to display all warnings.
     var paragraph = Blockly.Warning.textToDom_(this.getText());