diff --git a/core/components/component.js b/core/components/component.js
index 0d985b7ef..cca8285d5 100644
--- a/core/components/component.js
+++ b/core/components/component.js
@@ -84,6 +84,13 @@ Blockly.Component = function() {
    * @private
    */
   this.childIndex_ = {};
+
+  /**
+   * Whether or not the component has been disposed.
+   * @type {boolean}
+   * @private
+   */
+  this.disposed_ = false;
 };
 
 
diff --git a/core/components/tree/basenode.js b/core/components/tree/basenode.js
index 4416c6b6a..6e10d71b8 100644
--- a/core/components/tree/basenode.js
+++ b/core/components/tree/basenode.js
@@ -114,7 +114,7 @@ Blockly.utils.object.inherits(Blockly.tree.BaseNode, Blockly.Component);
  *            cssExpandedFolderIcon:string,
  *            cssCollapsedFolderIcon:string,
  *            cssFileIcon:string,
- *            cssSelectedRow:string
+ *            cssSelectedRow:string,
  *          }}
  */
 Blockly.tree.BaseNode.Config;
@@ -193,7 +193,7 @@ Blockly.tree.BaseNode.prototype.initAccessibility = function() {
 Blockly.tree.BaseNode.prototype.createDom = function() {
   var element = document.createElement('div');
   element.appendChild(this.toDom());
-  this.setElementInternal(/** @type {!Element} */ (element));
+  this.setElementInternal(/** @type {!HTMLElement} */ (element));
 };
 
 
@@ -368,6 +368,16 @@ Blockly.tree.BaseNode.prototype.getChildren = function() {
   return children;
 };
 
+/**
+ * Returns the node's parent, if any.
+ * @return {?Blockly.tree.BaseNode} The parent node.
+ * @protected
+ */
+Blockly.tree.BaseNode.prototype.getParent = function() {
+  return /** @type {Blockly.tree.BaseNode} */ (
+    Blockly.tree.BaseNode.superClass_.getParent.call(this));
+};
+
 /**
  * @return {Blockly.tree.BaseNode} The previous sibling of this node.
  * @protected
@@ -622,7 +632,7 @@ Blockly.tree.BaseNode.prototype.getBackgroundPosition = function() {
 };
 
 /**
- * @return {Element} The element for the tree node.
+ * @return {HTMLElement} The element for the tree node.
  * @override
  */
 Blockly.tree.BaseNode.prototype.getElement = function() {
@@ -631,7 +641,7 @@ Blockly.tree.BaseNode.prototype.getElement = function() {
     el = document.getElementById(this.getId());
     this.setElementInternal(el);
   }
-  return el;
+  return /** @type {!HTMLElement} */ (el);
 };
 
 /**
diff --git a/core/components/tree/treecontrol.js b/core/components/tree/treecontrol.js
index 37f8dc779..97ea3e39d 100644
--- a/core/components/tree/treecontrol.js
+++ b/core/components/tree/treecontrol.js
@@ -59,6 +59,20 @@ Blockly.tree.TreeControl = function(toolbox, config) {
    * @private
    */
   this.selectedItem_ = this;
+
+  /**
+   * A handler that's triggered before a node is selected.
+   * @type {?function(Blockly.tree.BaseNode):boolean}
+   * @private
+   */
+  this.onBeforeSelected_ = null;
+
+  /**
+   * A handler that's triggered before a node is selected.
+   * @type {?function(Blockly.tree.BaseNode, Blockly.tree.BaseNode):?}
+   * @private
+   */
+  this.onAfterSelected_ = null;
 };
 Blockly.utils.object.inherits(Blockly.tree.TreeControl, Blockly.tree.BaseNode);
 
@@ -123,11 +137,6 @@ Blockly.tree.TreeControl.prototype.getCalculatedIconClass = function() {
   if (!expanded && iconClass) {
     return iconClass;
   }
-
-  // fall back on default icons
-  if (expanded && this.config_.cssExpandedRootIcon) {
-    return this.config_.cssTreeIcon + ' ' + this.config_.cssExpandedRootIcon;
-  }
   return '';
 };
 
diff --git a/core/components/tree/treenode.js b/core/components/tree/treenode.js
index 455e7b0f2..c6aa3f2d2 100644
--- a/core/components/tree/treenode.js
+++ b/core/components/tree/treenode.js
@@ -32,6 +32,13 @@ goog.require('Blockly.utils.KeyCodes');
 Blockly.tree.TreeNode = function(toolbox, content, config) {
   this.toolbox_ = toolbox;
   Blockly.tree.BaseNode.call(this, content, config);
+
+  /**
+   * A handler that's triggered when the size of node has changed.
+   * @type {?function():?}
+   * @private
+   */
+  this.onSizeChanged_ = null;
 };
 Blockly.utils.object.inherits(Blockly.tree.TreeNode, Blockly.tree.BaseNode);
 
diff --git a/core/menu.js b/core/menu.js
index 578b6cbf3..a1621e83b 100644
--- a/core/menu.js
+++ b/core/menu.js
@@ -114,7 +114,7 @@ Blockly.Menu.prototype.addChild = function(menuItem) {
  * @param {!Element} container Element upon which to append this menu.
  */
 Blockly.Menu.prototype.render = function(container) {
-  var element = document.createElement('div');
+  var element = /** @type {!HTMLDivElement} */ (document.createElement('div'));
   // goog-menu is deprecated, use blocklyMenu.  May 2020.
   element.className = 'blocklyMenu goog-menu blocklyNonSelectable';
   element.tabIndex = 0;
@@ -215,7 +215,6 @@ Blockly.Menu.prototype.dispose = function() {
   for (var i = 0, menuItem; (menuItem = this.menuItems_[i]); i++) {
     menuItem.dispose();
   }
-  this.menuItems_length = 0;
   this.element_ = null;
 };
 
diff --git a/core/menuitem.js b/core/menuitem.js
index d483dcd45..ab93aec33 100644
--- a/core/menuitem.js
+++ b/core/menuitem.js
@@ -82,6 +82,13 @@ Blockly.MenuItem = function(content, opt_value) {
    */
   this.checked_ = false;
 
+  /**
+   * Is this menu item currently highlighted.
+   * @type {boolean}
+   * @private
+   */
+  this.highlight_ = false;
+
   /**
    * Bound function to call when this menu item is clicked.
    * @type {Function}