diff --git a/core/block.js b/core/block.js
index dd44dce1d..895c77c1b 100644
--- a/core/block.js
+++ b/core/block.js
@@ -1814,7 +1814,7 @@ Blockly.Block.prototype.getInputTargetBlock = function(name) {
 
 /**
  * Returns the comment on this block (or null if there is no comment).
- * @return {string} Block's comment.
+ * @return {?string} Block's comment.
  */
 Blockly.Block.prototype.getCommentText = function() {
   return this.commentModel.text;
diff --git a/core/block_drag_surface.js b/core/block_drag_surface.js
index ffdf54729..5c33b5273 100644
--- a/core/block_drag_surface.js
+++ b/core/block_drag_surface.js
@@ -173,7 +173,7 @@ Blockly.BlockDragSurfaceSvg.prototype.translateSurface = function(x, y) {
  * @return {!Blockly.utils.Coordinate} Current translation of the surface.
  */
 Blockly.BlockDragSurfaceSvg.prototype.getSurfaceTranslation = function() {
-  var xy = Blockly.utils.getRelativeXY(this.SVG_);
+  var xy = Blockly.utils.getRelativeXY(/** @type {!SVGElement} */ (this.SVG_));
   return new Blockly.utils.Coordinate(xy.x / this.scale_, xy.y / this.scale_);
 };
 
@@ -189,11 +189,11 @@ Blockly.BlockDragSurfaceSvg.prototype.getGroup = function() {
 /**
  * Get the current blocks on the drag surface, if any (primarily
  * for BlockSvg.getRelativeToSurfaceXY).
- * @return {!Element|undefined} Drag surface block DOM element, or undefined
- * if no blocks exist.
+ * @return {Element} Drag surface block DOM element, or undefined if no blocks
+ * exist.
  */
 Blockly.BlockDragSurfaceSvg.prototype.getCurrentBlock = function() {
-  return this.dragGroup_.firstChild;
+  return /** @type {Element} */ (this.dragGroup_.firstChild);
 };
 
 /**
diff --git a/core/block_svg.js b/core/block_svg.js
index 7119d7d23..5c34f64ae 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -56,7 +56,7 @@ goog.require('Blockly.Warning');
 Blockly.BlockSvg = function(workspace, prototypeName, opt_id) {
   // Create core elements for the block.
   /**
-   * @type {SVGElement}
+   * @type {!SVGElement}
    * @private
    */
   this.svgGroup_ = Blockly.utils.dom.createSvgElement('g', {}, null);
@@ -440,7 +440,7 @@ Blockly.BlockSvg.prototype.getRelativeToSurfaceXY = function() {
         x += surfaceTranslation.x;
         y += surfaceTranslation.y;
       }
-      element = element.parentNode;
+      element = /** @type {!SVGElement} */ (element.parentNode);
     } while (element && element != this.workspace.getCanvas() &&
         element != dragSurfaceGroup);
   }
@@ -997,7 +997,7 @@ Blockly.BlockSvg.prototype.setInsertionMarker = function(insertionMarker) {
 
 /**
  * Return the root node of the SVG or null if none exists.
- * @return {SVGElement} The root SVG node (probably a group).
+ * @return {!SVGElement} The root SVG node (probably a group).
  */
 Blockly.BlockSvg.prototype.getSvgRoot = function() {
   return this.svgGroup_;
diff --git a/core/blockly.js b/core/blockly.js
index 02966ed09..11513dddc 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -363,7 +363,7 @@ Blockly.hideChaff = function(opt_allowToolbox) {
  * @return {!Blockly.Workspace} The main workspace.
  */
 Blockly.getMainWorkspace = function() {
-  return Blockly.mainWorkspace;
+  return /** @type {!Blockly.Workspace} */ (Blockly.mainWorkspace);
 };
 
 /**
@@ -396,7 +396,7 @@ Blockly.confirm = function(message, callback) {
  * recommend testing mobile when overriding this.
  * @param {string} message The message to display to the user.
  * @param {string} defaultValue The value to initialize the prompt with.
- * @param {!function(string)} callback The callback for handling user response.
+ * @param {!function(?string)} callback The callback for handling user response.
  */
 Blockly.prompt = function(message, defaultValue, callback) {
   callback(prompt(message, defaultValue));
diff --git a/core/contextmenu.js b/core/contextmenu.js
index 10330e9ff..48aa337ea 100644
--- a/core/contextmenu.js
+++ b/core/contextmenu.js
@@ -279,7 +279,7 @@ Blockly.ContextMenu.blockCommentOption = function(block) {
     enabled: !Blockly.utils.userAgent.IE
   };
   // If there's already a comment, add an option to delete it.
-  if (block.comment) {
+  if (block.getCommentIcon()) {
     commentOption.text = Blockly.Msg['REMOVE_COMMENT'];
     commentOption.callback = function() {
       block.setCommentText(null);
diff --git a/core/events.js b/core/events.js
index f52a838c2..d58771afa 100644
--- a/core/events.js
+++ b/core/events.js
@@ -391,7 +391,7 @@ Blockly.Events.fromJson = function(json, workspace) {
       event = new Blockly.Events.CommentDelete(null);
       break;
     case Blockly.Events.FINISHED_LOADING:
-      event = new Blockly.Events.FinishedLoading(null);
+      event = new Blockly.Events.FinishedLoading(workspace);
       break;
     default:
       throw Error('Unknown event type.');
diff --git a/core/extensions.js b/core/extensions.js
index 3f43a3ca8..c410bb3e9 100644
--- a/core/extensions.js
+++ b/core/extensions.js
@@ -87,7 +87,7 @@ Blockly.Extensions.registerMixin = function(name, mixinObj) {
  * @param {!Object} mixinObj The values to mix in.
  * @param {(function())=} opt_helperFn An optional function to apply after
  *     mixing in the object.
- * @param {Array.<string>=} opt_blockList A list of blocks to appear in the
+ * @param {!Array.<string>=} opt_blockList A list of blocks to appear in the
  *     flyout of the mutator dialog.
  * @throws {Error} if the mutation is invalid or can't be applied to the block.
  */
@@ -114,7 +114,7 @@ Blockly.Extensions.registerMutator = function(name, mixinObj, opt_helperFn,
       if (!Blockly.Mutator) {
         throw Error(errorPrefix + 'Missing require for Blockly.Mutator');
       }
-      this.setMutator(new Blockly.Mutator(opt_blockList));
+      this.setMutator(new Blockly.Mutator(opt_blockList || []));
     }
     // Mixin the object.
     this.mixin(mixinObj);
@@ -165,7 +165,8 @@ Blockly.Extensions.apply = function(name, block, isMutator) {
     var errorPrefix = 'Error after applying mutator "' + name + '": ';
     Blockly.Extensions.checkBlockHasMutatorProperties_(errorPrefix, block);
   } else {
-    if (!Blockly.Extensions.mutatorPropertiesMatch_(mutatorProperties, block)) {
+    if (!Blockly.Extensions.mutatorPropertiesMatch_(
+        /** @type {!Array.<Object>} */ (mutatorProperties), block)) {
       throw Error('Error when applying extension "' + name + '": ' +
           'mutation properties changed when applying a non-mutator extension.');
     }
@@ -359,7 +360,7 @@ Blockly.Extensions.buildTooltipForDropdown = function(dropdownName,
     }
 
     this.setTooltip(function() {
-      var value = this.getFieldValue(dropdownName);
+      var value = String(this.getFieldValue(dropdownName));
       var tooltip = lookupTable[value];
       if (tooltip == null) {
         if (blockTypesChecked.indexOf(this.type) == -1) {
diff --git a/core/grid.js b/core/grid.js
index 3b036f493..72367c10b 100644
--- a/core/grid.js
+++ b/core/grid.js
@@ -64,14 +64,15 @@ Blockly.Grid = function(pattern, options) {
    * @type {SVGElement}
    * @private
    */
-  this.line1_ = pattern.firstChild;
+  this.line1_ = /** @type {SVGElement} */ (pattern.firstChild);
 
   /**
    * The vertical grid line, if it exists.
    * @type {SVGElement}
    * @private
    */
-  this.line2_ = this.line1_ && this.line1_.nextSibling;
+  this.line2_ = this.line1_ &&
+    (/** @type {SVGElement} */ (this.line1_.nextSibling));
 
   /**
    * Whether blocks should snap to the grid.
@@ -154,7 +155,7 @@ Blockly.Grid.prototype.update = function(scale) {
 /**
  * Set the attributes on one of the lines in the grid.  Use this to update the
  * length and stroke width of the grid lines.
- * @param {!SVGElement} line Which line to update.
+ * @param {SVGElement} line Which line to update.
  * @param {number} width The new stroke size (in px).
  * @param {number} x1 The new x start position of the line (in px).
  * @param {number} x2 The new x end position of the line (in px).
diff --git a/core/keyboard_nav/ast_node.js b/core/keyboard_nav/ast_node.js
index ed74df6a7..2721b8c4e 100644
--- a/core/keyboard_nav/ast_node.js
+++ b/core/keyboard_nav/ast_node.js
@@ -293,7 +293,7 @@ Blockly.ASTNode.prototype.findNextForField_ = function() {
   var location = /** @type {!Blockly.Field} */ (this.location_);
   var input = location.getParentInput();
   var block = location.getSourceBlock();
-  var curIdx = block.inputList.indexOf(input);
+  var curIdx = block.inputList.indexOf(/** @type {!Blockly.Input} */ (input));
   var fieldIdx = input.fieldRow.indexOf(location) + 1;
   for (var i = curIdx, newInput; newInput = block.inputList[i]; i++) {
     var fieldRow = newInput.fieldRow;
@@ -347,7 +347,8 @@ Blockly.ASTNode.prototype.findPrevForField_ = function() {
   var location = /** @type {!Blockly.Field} */ (this.location_);
   var parentInput = location.getParentInput();
   var block = location.getSourceBlock();
-  var curIdx = block.inputList.indexOf(parentInput);
+  var curIdx = block.inputList.indexOf(
+      /** @type {!Blockly.Input} */ (parentInput));
   var fieldIdx = parentInput.fieldRow.indexOf(location) - 1;
   for (var i = curIdx, input; input = block.inputList[i]; i--) {
     if (input.connection && input !== parentInput) {
diff --git a/core/workspace.js b/core/workspace.js
index 59a5e845a..2119c8d17 100644
--- a/core/workspace.js
+++ b/core/workspace.js
@@ -109,7 +109,7 @@ Blockly.Workspace = function(opt_options) {
    * A FieldVariable must always refer to a Blockly.VariableModel.  We reconcile
    * these by tracking "potential" variables in the flyout.  These variables
    * become real when references to them are dragged into the main workspace.
-   * @type {!Blockly.VariableMap}
+   * @type {Blockly.VariableMap}
    * @private
    */
   this.potentialVariableMap_ = null;
@@ -246,9 +246,11 @@ Blockly.Workspace.prototype.refreshTheme = function() {
 Blockly.Workspace.prototype.updateBlockStyles_ = function(blocks) {
   for (var i = 0, block; block = blocks[i]; i++) {
     var blockStyleName = block.getStyleName();
-    block.setStyle(blockStyleName);
-    if (block.mutator) {
-      block.mutator.updateBlockStyle(blockStyleName);
+    if (blockStyleName) {
+      block.setStyle(blockStyleName);
+      if (block.mutator) {
+        block.mutator.updateBlockStyle();
+      }
     }
   }
 };
@@ -861,7 +863,7 @@ Blockly.Workspace.prototype.createPotentialVariableMap = function() {
 
 /**
  * Return the map of all variables on the workspace.
- * @return {Blockly.VariableMap} The variable map.
+ * @return {!Blockly.VariableMap} The variable map.
  */
 Blockly.Workspace.prototype.getVariableMap = function() {
   return this.variableMap_;
@@ -869,7 +871,7 @@ Blockly.Workspace.prototype.getVariableMap = function() {
 
 /**
  * Set the map of all variables on the workspace.
- * @param {Blockly.VariableMap} variableMap The variable map.
+ * @param {!Blockly.VariableMap} variableMap The variable map.
  * @package
  */
 Blockly.Workspace.prototype.setVariableMap = function(variableMap) {
diff --git a/core/workspace_audio.js b/core/workspace_audio.js
index 256cd5166..1c24f742b 100644
--- a/core/workspace_audio.js
+++ b/core/workspace_audio.js
@@ -48,7 +48,6 @@ Blockly.WorkspaceAudio = function(parentWorkspace) {
   /**
    * Database of pre-loaded sounds.
    * @private
-   * @const
    */
   this.SOUNDS_ = Object.create(null);
 };
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index aee610986..8c676431a 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -531,7 +531,7 @@ Blockly.WorkspaceSvg.prototype.isVisible = function() {
  * Return the absolute coordinates of the top-left corner of this element,
  * scales that after canvas SVG element, if it's a descendant.
  * The origin (0,0) is the top-left corner of the Blockly SVG.
- * @param {!Element} element Element to find the coordinates of.
+ * @param {!SVGElement} element SVG element to find the coordinates of.
  * @return {!Blockly.utils.Coordinate} Object with .x and .y properties.
  * @package
  */
@@ -554,7 +554,7 @@ Blockly.WorkspaceSvg.prototype.getSvgXY = function(element) {
     }
     x += xy.x * scale;
     y += xy.y * scale;
-    element = /** @type {!Element} */ (element.parentNode);
+    element = /** @type {!SVGElement} */ (element.parentNode);
   } while (element && element != this.getParentSvg());
   return new Blockly.utils.Coordinate(x, y);
 };
@@ -1335,7 +1335,7 @@ Blockly.WorkspaceSvg.prototype.deleteVariableById = function(id) {
  *     their type. This will default to '' which is a specific type.
  * @param {?string=} opt_id The unique ID of the variable. This will default to
  *     a UUID.
- * @return {Blockly.VariableModel} The newly created variable.
+ * @return {!Blockly.VariableModel} The newly created variable.
  * @package
  */
 Blockly.WorkspaceSvg.prototype.createVariable = function(name,
@@ -1420,7 +1420,8 @@ Blockly.WorkspaceSvg.prototype.moveDrag = function(e) {
   // Fix scale of mouse event.
   point.x /= this.scale;
   point.y /= this.scale;
-  return Blockly.utils.Coordinate.sum(this.dragDeltaXY_, point);
+  return Blockly.utils.Coordinate.sum(
+      /** @type {!Blockly.utils.Coordinate} */ (this.dragDeltaXY_), point);
 };
 
 /**