diff --git a/core/bubble.ts b/core/bubble.ts
index 9b5fe1396..f9a70eddd 100644
--- a/core/bubble.ts
+++ b/core/bubble.ts
@@ -68,39 +68,29 @@ export class Bubble implements IBubble {
 
   /** Mouse move event data. */
   private static onMouseMoveWrapper_: browserEvents.Data|null = null;
-  workspace_: AnyDuringMigration;
-  content_: AnyDuringMigration;
-  shape_: AnyDuringMigration;
+  workspace_: WorkspaceSvg;
+  content_: SVGElement;
+  shape_: SVGElement;
 
   /** Flag to stop incremental rendering during construction. */
   private readonly rendered_: boolean;
 
   /** The SVG group containing all parts of the bubble. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGGElement'.
-  private bubbleGroup_: SVGGElement = null as AnyDuringMigration;
+  private bubbleGroup_: SVGGElement|null = null;
 
   /**
    * The SVG path for the arrow from the bubble to the icon on the block.
    */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGPathElement'.
-  private bubbleArrow_: SVGPathElement = null as AnyDuringMigration;
+  private bubbleArrow_: SVGPathElement|null = null;
 
   /** The SVG rect for the main body of the bubble. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGRectElement'.
-  private bubbleBack_: SVGRectElement = null as AnyDuringMigration;
+  private bubbleBack_: SVGRectElement|null = null;
 
   /** The SVG group for the resize hash marks on some bubbles. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGGElement'.
-  private resizeGroup_: SVGGElement = null as AnyDuringMigration;
+  private resizeGroup_: SVGGElement|null = null;
 
   /** Absolute coordinate of anchor point, in workspace coordinates. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'Coordinate'.
-  private anchorXY_: Coordinate = null as AnyDuringMigration;
+  private anchorXY_!: Coordinate;
 
   /**
    * Relative X coordinate of bubble with respect to the anchor's centre,
@@ -125,10 +115,10 @@ export class Bubble implements IBubble {
   private autoLayout_ = true;
 
   /** Method to call on resize of bubble. */
-  private resizeCallback_: (() => AnyDuringMigration)|null = null;
+  private resizeCallback_: (() => void)|null = null;
 
   /** Method to call on move of bubble. */
-  private moveCallback_: (() => AnyDuringMigration)|null = null;
+  private moveCallback_: (() => void)|null = null;
 
   /** Mouse down on bubbleBack_ event data. */
   private onMouseDownBubbleWrapper_: browserEvents.Data|null = null;
@@ -142,7 +132,7 @@ export class Bubble implements IBubble {
    * @internal
    */
   disposed = false;
-  private arrow_radians_: AnyDuringMigration;
+  private arrow_radians_: number;
 
   /**
    * @param workspace The workspace on which to draw the bubble.
@@ -260,9 +250,7 @@ export class Bubble implements IBubble {
           },
           this.resizeGroup_);
     } else {
-      // AnyDuringMigration because:  Type 'null' is not assignable to type
-      // 'SVGGElement'.
-      this.resizeGroup_ = null as AnyDuringMigration;
+      this.resizeGroup_ = null;
     }
 
     if (!this.workspace_.options.readOnly) {
@@ -290,7 +278,7 @@ export class Bubble implements IBubble {
    * @param id ID of block.
    */
   setSvgId(id: string) {
-    this.bubbleGroup_.setAttribute('data-block-id', id);
+    this.bubbleGroup_?.setAttribute('data-block-id', id);
   }
 
   /**
@@ -374,20 +362,16 @@ export class Bubble implements IBubble {
    * Register a function as a callback event for when the bubble is resized.
    * @param callback The function to call on resize.
    */
-  registerResizeEvent(callback: Function) {
-    // AnyDuringMigration because:  Type 'Function' is not assignable to type
-    // '() => any'.
-    this.resizeCallback_ = callback as AnyDuringMigration;
+  registerResizeEvent(callback: () => void) {
+    this.resizeCallback_ = callback;
   }
 
   /**
    * Register a function as a callback event for when the bubble is moved.
    * @param callback The function to call on move.
    */
-  registerMoveEvent(callback: Function) {
-    // AnyDuringMigration because:  Type 'Function' is not assignable to type
-    // '() => any'.
-    this.moveCallback_ = callback as AnyDuringMigration;
+  registerMoveEvent(callback: () => void) {
+    this.moveCallback_ = callback;
   }
 
   /**
@@ -396,9 +380,9 @@ export class Bubble implements IBubble {
    * @internal
    */
   promote(): boolean {
-    const svgGroup = this.bubbleGroup_.parentNode;
-    if (svgGroup!.lastChild !== this.bubbleGroup_) {
-      svgGroup!.appendChild(this.bubbleGroup_);
+    const svgGroup = this.bubbleGroup_?.parentNode;
+    if (svgGroup?.lastChild !== this.bubbleGroup_ && this.bubbleGroup_) {
+      svgGroup?.appendChild(this.bubbleGroup_);
       return true;
     }
     return false;
@@ -630,7 +614,7 @@ export class Bubble implements IBubble {
    * @internal
    */
   moveTo(x: number, y: number) {
-    this.bubbleGroup_.setAttribute(
+    this.bubbleGroup_?.setAttribute(
         'transform', 'translate(' + x + ',' + y + ')');
   }
 
@@ -665,12 +649,8 @@ export class Bubble implements IBubble {
     height = Math.max(height, doubleBorderWidth + 20);
     this.width_ = width;
     this.height_ = height;
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.bubbleBack_.setAttribute('width', width as AnyDuringMigration);
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.bubbleBack_.setAttribute('height', height as AnyDuringMigration);
+    this.bubbleBack_?.setAttribute('width', width.toString());
+    this.bubbleBack_?.setAttribute('height', height.toString());
     if (this.resizeGroup_) {
       if (this.workspace_.RTL) {
         // Mirror the resize group.
@@ -765,7 +745,7 @@ export class Bubble implements IBubble {
           ',' + (baseY2 + swirlRise) + ' ' + baseX2 + ',' + baseY2);
     }
     steps.push('z');
-    this.bubbleArrow_.setAttribute('d', steps.join(' '));
+    this.bubbleArrow_?.setAttribute('d', steps.join(' '));
   }
 
   /**
@@ -773,8 +753,8 @@ export class Bubble implements IBubble {
    * @param hexColour Hex code of colour.
    */
   setColour(hexColour: string) {
-    this.bubbleBack_.setAttribute('fill', hexColour);
-    this.bubbleArrow_.setAttribute('fill', hexColour);
+    this.bubbleBack_?.setAttribute('fill', hexColour);
+    this.bubbleArrow_?.setAttribute('fill', hexColour);
   }
 
   /** Dispose of this bubble. */
diff --git a/core/clipboard.ts b/core/clipboard.ts
index 2c43c8d29..af95c9677 100644
--- a/core/clipboard.ts
+++ b/core/clipboard.ts
@@ -79,7 +79,8 @@ export function duplicate(toDuplicate: ICopyable): ICopyable|null {
 function duplicateInternal(toDuplicate: ICopyable): ICopyable|null {
   const oldCopyData = copyData;
   copy(toDuplicate);
-  const pastedThing = toDuplicate.toCopyData().source.paste(copyData!.saveInfo);
+  const pastedThing =
+      toDuplicate.toCopyData()?.source?.paste(copyData!.saveInfo) ?? null;
   copyData = oldCopyData;
   return pastedThing;
 }
diff --git a/core/connection_checker.ts b/core/connection_checker.ts
index c03ec5a94..151309c80 100644
--- a/core/connection_checker.ts
+++ b/core/connection_checker.ts
@@ -207,9 +207,7 @@ export class ConnectionChecker implements IConnectionChecker {
    */
   doDragChecks(a: RenderedConnection, b: RenderedConnection, distance: number):
       boolean {
-    // AnyDuringMigration because:  Argument of type 'RenderedConnection' is not
-    // assignable to parameter of type 'Connection'.
-    if (a.distanceFrom(b as AnyDuringMigration) > distance) {
+    if (a.distanceFrom(b) > distance) {
       return false;
     }
 
@@ -220,9 +218,7 @@ export class ConnectionChecker implements IConnectionChecker {
 
     switch (b.type) {
       case ConnectionType.PREVIOUS_STATEMENT:
-        // AnyDuringMigration because:  Argument of type 'RenderedConnection' is
-        // not assignable to parameter of type 'Connection'.
-        return this.canConnectToPrevious_(a as AnyDuringMigration, b);
+        return this.canConnectToPrevious_(a, b);
       case ConnectionType.OUTPUT_VALUE: {
         // Don't offer to connect an already connected left (male) value plug to
         // an available right (female) value plug.
@@ -259,9 +255,7 @@ export class ConnectionChecker implements IConnectionChecker {
     }
 
     // Don't let blocks try to connect to themselves or ones they nest.
-    // AnyDuringMigration because:  Argument of type 'RenderedConnection' is not
-    // assignable to parameter of type 'Connection'.
-    if (common.draggingConnections.indexOf(b as AnyDuringMigration) !== -1) {
+    if (common.draggingConnections.indexOf(b) !== -1) {
       return false;
     }
 
diff --git a/core/connection_db.ts b/core/connection_db.ts
index 72ef93152..dfde386b6 100644
--- a/core/connection_db.ts
+++ b/core/connection_db.ts
@@ -162,7 +162,7 @@ export class ConnectionDB {
       pointerMid = Math.floor((pointerMin + pointerMax) / 2);
     }
 
-    const neighbours: AnyDuringMigration[] = [];
+    const neighbours: RenderedConnection[] = [];
     /**
      * Computes if the current connection is within the allowed radius of
      * another connection. This function is a closure and has access to outside
@@ -220,12 +220,10 @@ export class ConnectionDB {
    */
   searchForClosest(
       conn: RenderedConnection, maxRadius: number,
-      dxy: Coordinate): {connection: RenderedConnection, radius: number} {
+      dxy: Coordinate): {connection: RenderedConnection|null, radius: number} {
     if (!this.connections_.length) {
       // Don't bother.
-      // AnyDuringMigration because:  Type 'null' is not assignable to type
-      // 'RenderedConnection'.
-      return {connection: null as AnyDuringMigration, radius: maxRadius};
+      return {connection: null, radius: maxRadius};
     }
 
     // Stash the values of x and y from before the drag.
@@ -250,9 +248,7 @@ export class ConnectionDB {
       temp = this.connections_[pointerMin];
       if (this.connectionChecker.canConnect(conn, temp, true, bestRadius)) {
         bestConnection = temp;
-        // AnyDuringMigration because:  Argument of type 'RenderedConnection' is
-        // not assignable to parameter of type 'Connection'.
-        bestRadius = temp.distanceFrom(conn as AnyDuringMigration);
+        bestRadius = temp.distanceFrom(conn);
       }
       pointerMin--;
     }
@@ -263,9 +259,7 @@ export class ConnectionDB {
       temp = this.connections_[pointerMax];
       if (this.connectionChecker.canConnect(conn, temp, true, bestRadius)) {
         bestConnection = temp;
-        // AnyDuringMigration because:  Argument of type 'RenderedConnection' is
-        // not assignable to parameter of type 'Connection'.
-        bestRadius = temp.distanceFrom(conn as AnyDuringMigration);
+        bestRadius = temp.distanceFrom(conn);
       }
       pointerMax++;
     }
@@ -274,12 +268,7 @@ export class ConnectionDB {
     conn.x = baseX;
     conn.y = baseY;
     // If there were no valid connections, bestConnection will be null.
-    // AnyDuringMigration because:  Type 'RenderedConnection | null' is not
-    // assignable to type 'RenderedConnection'.
-    return {
-      connection: bestConnection as AnyDuringMigration,
-      radius: bestRadius
-    };
+    return {connection: bestConnection, radius: bestRadius};
   }
 
   /**
diff --git a/core/contextmenu_items.ts b/core/contextmenu_items.ts
index df8c24692..e605a7e47 100644
--- a/core/contextmenu_items.ts
+++ b/core/contextmenu_items.ts
@@ -114,7 +114,7 @@ function toggleOption_(shouldCollapse: boolean, topBlocks: BlockSvg[]) {
   const DELAY = 10;
   let ms = 0;
   let timeoutCounter = 0;
-  function timeoutFn(block: AnyDuringMigration) {
+  function timeoutFn(block: BlockSvg) {
     timeoutCounter--;
     block.setCollapsed(shouldCollapse);
     if (timeoutCounter === 0) {
@@ -123,13 +123,11 @@ function toggleOption_(shouldCollapse: boolean, topBlocks: BlockSvg[]) {
   }
   Events.setGroup(true);
   for (let i = 0; i < topBlocks.length; i++) {
-    let block = topBlocks[i];
+    let block: BlockSvg|null = topBlocks[i];
     while (block) {
       timeoutCounter++;
       setTimeout(timeoutFn.bind(null, block), ms);
-      // AnyDuringMigration because:  Type 'BlockSvg | null' is not assignable
-      // to type 'BlockSvg'.
-      block = block.getNextBlock() as AnyDuringMigration;
+      block = block.getNextBlock();
       ms += DELAY;
     }
   }
@@ -148,14 +146,12 @@ export function registerCollapse() {
       if (scope.workspace!.options.collapse) {
         const topBlocks = scope.workspace!.getTopBlocks(false);
         for (let i = 0; i < topBlocks.length; i++) {
-          let block = topBlocks[i];
+          let block: BlockSvg|null = topBlocks[i];
           while (block) {
             if (!block.isCollapsed()) {
               return 'enabled';
             }
-            // AnyDuringMigration because:  Type 'BlockSvg | null' is not
-            // assignable to type 'BlockSvg'.
-            block = block.getNextBlock() as AnyDuringMigration;
+            block = block.getNextBlock();
           }
         }
         return 'disabled';
@@ -185,14 +181,12 @@ export function registerExpand() {
       if (scope.workspace!.options.collapse) {
         const topBlocks = scope.workspace!.getTopBlocks(false);
         for (let i = 0; i < topBlocks.length; i++) {
-          let block = topBlocks[i];
+          let block: BlockSvg|null = topBlocks[i];
           while (block) {
             if (block.isCollapsed()) {
               return 'enabled';
             }
-            // AnyDuringMigration because:  Type 'BlockSvg | null' is not
-            // assignable to type 'BlockSvg'.
-            block = block.getNextBlock() as AnyDuringMigration;
+            block = block.getNextBlock();
           }
         }
         return 'disabled';
@@ -231,7 +225,7 @@ function addDeletableBlocks_(block: BlockSvg, deleteList: BlockSvg[]) {
  * @return list of blocks to delete.
  */
 function getDeletableBlocks_(workspace: WorkspaceSvg): BlockSvg[] {
-  const deleteList: AnyDuringMigration[] = [];
+  const deleteList: BlockSvg[] = [];
   const topBlocks = workspace.getTopBlocks(true);
   for (let i = 0; i < topBlocks.length; i++) {
     addDeletableBlocks_(topBlocks[i], deleteList);
@@ -265,12 +259,10 @@ function deleteNext_(deleteList: BlockSvg[], eventGroup: string) {
  * @alias Blockly.ContextMenuItems.registerDeleteAll
  */
 export function registerDeleteAll() {
-  // AnyDuringMigration because:  Type '(scope: Scope) => string | undefined' is
-  // not assignable to type 'string | ((p1: Scope) => string)'.
   const deleteOption: RegistryItem = {
     displayText(scope: Scope) {
       if (!scope.workspace) {
-        return;
+        return '';
       }
       const deletableBlocksLength = getDeletableBlocks_(scope.workspace).length;
       if (deletableBlocksLength === 1) {
@@ -282,7 +274,7 @@ export function registerDeleteAll() {
     },
     preconditionFn(scope: Scope) {
       if (!scope.workspace) {
-        return;
+        return 'disabled';
       }
       const deletableBlocksLength = getDeletableBlocks_(scope.workspace).length;
       return deletableBlocksLength > 0 ? 'enabled' : 'disabled';
@@ -310,7 +302,7 @@ export function registerDeleteAll() {
     scopeType: ContextMenuRegistry.ScopeType.WORKSPACE,
     id: 'workspaceDelete',
     weight: 6,
-  } as AnyDuringMigration;
+  };
   ContextMenuRegistry.registry.register(deleteOption);
 }
 /** Registers all workspace-scoped context menu items. */
diff --git a/core/grid.ts b/core/grid.ts
index 2ccd37473..1933635ba 100644
--- a/core/grid.ts
+++ b/core/grid.ts
@@ -20,6 +20,7 @@ goog.declareModuleId('Blockly.Grid');
 import * as dom from './utils/dom.js';
 import {Svg} from './utils/svg.js';
 import * as userAgent from './utils/useragent.js';
+import {GridOptions} from './blockly_options.js';
 
 
 /**
@@ -44,12 +45,12 @@ export class Grid {
    *     See grid documentation:
    *     https://developers.google.com/blockly/guides/configure/web/grid
    */
-  constructor(private pattern: SVGElement, options: AnyDuringMigration) {
+  constructor(private pattern: SVGElement, options: GridOptions) {
     /** The spacing of the grid lines (in px). */
-    this.spacing_ = options['spacing'];
+    this.spacing_ = options['spacing'] ?? 0;
 
     /** How long the grid lines should be (in px). */
-    this.length_ = options['length'];
+    this.length_ = options['length'] ?? 1;
 
     /** The horizontal grid line, if it exists. */
     this.line1_ = pattern.firstChild as SVGElement;
@@ -58,18 +59,7 @@ export class Grid {
     this.line2_ = this.line1_ && this.line1_.nextSibling as SVGElement;
 
     /** Whether blocks should snap to the grid. */
-    this.snapToGrid_ = options['snap'];
-  }
-
-  /**
-   * Dispose of this grid and unlink from the DOM.
-   * @suppress {checkTypes}
-   * @internal
-   */
-  dispose() {
-    // AnyDuringMigration because:  Type 'null' is not assignable to type
-    // 'SVGElement'.
-    this.pattern = null as AnyDuringMigration;
+    this.snapToGrid_ = options['snap'] ?? false;
   }
 
   /**
@@ -110,12 +100,8 @@ export class Grid {
     // MSIE freaks if it sees a 0x0 pattern, so set empty patterns to 100x100.
     const safeSpacing = this.spacing_ * scale || 100;
 
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.pattern.setAttribute('width', safeSpacing as AnyDuringMigration);
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.pattern.setAttribute('height', safeSpacing as AnyDuringMigration);
+    this.pattern.setAttribute('width', safeSpacing.toString());
+    this.pattern.setAttribute('height', safeSpacing.toString());
 
     let half = Math.floor(this.spacing_ / 2) + 0.5;
     let start = half - this.length_ / 2;
@@ -143,21 +129,11 @@ export class Grid {
       line: SVGElement, width: number, x1: number, x2: number, y1: number,
       y2: number) {
     if (line) {
-      // AnyDuringMigration because:  Argument of type 'number' is not
-      // assignable to parameter of type 'string'.
-      line.setAttribute('stroke-width', width as AnyDuringMigration);
-      // AnyDuringMigration because:  Argument of type 'number' is not
-      // assignable to parameter of type 'string'.
-      line.setAttribute('x1', x1 as AnyDuringMigration);
-      // AnyDuringMigration because:  Argument of type 'number' is not
-      // assignable to parameter of type 'string'.
-      line.setAttribute('y1', y1 as AnyDuringMigration);
-      // AnyDuringMigration because:  Argument of type 'number' is not
-      // assignable to parameter of type 'string'.
-      line.setAttribute('x2', x2 as AnyDuringMigration);
-      // AnyDuringMigration because:  Argument of type 'number' is not
-      // assignable to parameter of type 'string'.
-      line.setAttribute('y2', y2 as AnyDuringMigration);
+      line.setAttribute('stroke-width', width.toString());
+      line.setAttribute('x1', x1.toString());
+      line.setAttribute('y1', y1.toString());
+      line.setAttribute('x2', x2.toString());
+      line.setAttribute('y2', y2.toString());
     }
   }
 
@@ -169,12 +145,8 @@ export class Grid {
    * @internal
    */
   moveTo(x: number, y: number) {
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.pattern.setAttribute('x', x as AnyDuringMigration);
-    // AnyDuringMigration because:  Argument of type 'number' is not assignable
-    // to parameter of type 'string'.
-    this.pattern.setAttribute('y', y as AnyDuringMigration);
+    this.pattern.setAttribute('x', x.toString());
+    this.pattern.setAttribute('y', y.toString());
 
     if (userAgent.IE || userAgent.EDGE) {
       // IE/Edge doesn't notice that the x/y offsets have changed.
@@ -191,9 +163,8 @@ export class Grid {
    * @return The SVG element for the grid pattern.
    * @internal
    */
-  static createDom(
-      rnd: string, gridOptions: AnyDuringMigration,
-      defs: SVGElement): SVGElement {
+  static createDom(rnd: string, gridOptions: GridOptions, defs: SVGElement):
+      SVGElement {
     /*
           <pattern id="blocklyGridPattern837493" patternUnits="userSpaceOnUse">
             <rect stroke="#888" />
@@ -205,10 +176,10 @@ export class Grid {
         {'id': 'blocklyGridPattern' + rnd, 'patternUnits': 'userSpaceOnUse'},
         defs);
     // x1, y1, x1, x2 properties will be set later in update.
-    if (gridOptions['length'] > 0 && gridOptions['spacing'] > 0) {
+    if ((gridOptions['length'] ?? 1) > 0 && (gridOptions['spacing'] ?? 0) > 0) {
       dom.createSvgElement(
           Svg.LINE, {'stroke': gridOptions['colour']}, gridPattern);
-      if (gridOptions['length'] > 1) {
+      if (gridOptions['length'] ?? 1 > 1) {
         dom.createSvgElement(
             Svg.LINE, {'stroke': gridOptions['colour']}, gridPattern);
       }
diff --git a/core/interfaces/i_ast_node_location_svg.ts b/core/interfaces/i_ast_node_location_svg.ts
index 758533d14..287e77919 100644
--- a/core/interfaces/i_ast_node_location_svg.ts
+++ b/core/interfaces/i_ast_node_location_svg.ts
@@ -27,11 +27,11 @@ export interface IASTNodeLocationSvg extends IASTNodeLocation {
    * Add the marker SVG to this node's SVG group.
    * @param markerSvg The SVG root of the marker to be added to the SVG group.
    */
-  setMarkerSvg: AnyDuringMigration;
+  setMarkerSvg(markerSvg: SVGElement|null): void;
 
   /**
    * Add the cursor SVG to this node's SVG group.
    * @param cursorSvg The SVG root of the cursor to be added to the SVG group.
    */
-  setCursorSvg: AnyDuringMigration;
+  setCursorSvg(cursorSvg: SVGElement|null): void;
 }
diff --git a/core/interfaces/i_ast_node_location_with_block.ts b/core/interfaces/i_ast_node_location_with_block.ts
index 727a1dca0..72e5dba12 100644
--- a/core/interfaces/i_ast_node_location_with_block.ts
+++ b/core/interfaces/i_ast_node_location_with_block.ts
@@ -22,6 +22,7 @@ goog.declareModuleId('Blockly.IASTNodeLocationWithBlock');
 // import '../block.js';
 
 import type {IASTNodeLocation} from './i_ast_node_location.js';
+import type {Block} from '../block.js';
 
 
 /**
@@ -33,5 +34,5 @@ export interface IASTNodeLocationWithBlock extends IASTNodeLocation {
    * Get the source block associated with this node.
    * @return The source block.
    */
-  getSourceBlock: AnyDuringMigration;
+  getSourceBlock(): Block;
 }
diff --git a/core/interfaces/i_autohideable.ts b/core/interfaces/i_autohideable.ts
index 2777c6b36..c1b81781e 100644
--- a/core/interfaces/i_autohideable.ts
+++ b/core/interfaces/i_autohideable.ts
@@ -30,5 +30,5 @@ export interface IAutoHideable extends IComponent {
    * @param onlyClosePopups Whether only popups should be closed.
    *   Flyouts should not be closed if this is true.
    */
-  autoHide: AnyDuringMigration;
+  autoHide(onlyClosePopups: boolean): void;
 }
diff --git a/core/interfaces/i_block_dragger.ts b/core/interfaces/i_block_dragger.ts
index 3e3a28ca7..7aa74f15c 100644
--- a/core/interfaces/i_block_dragger.ts
+++ b/core/interfaces/i_block_dragger.ts
@@ -13,6 +13,8 @@
  * @namespace Blockly.IBlockDragger
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {Coordinate} from '../utils/coordinate.js';
+import type {BlockSvg} from '../block_svg.js';
 goog.declareModuleId('Blockly.IBlockDragger');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -34,7 +36,7 @@ export interface IBlockDragger {
    *     at mouse down, in pixel units.
    * @param healStack Whether or not to heal the stack after disconnecting.
    */
-  startDrag: AnyDuringMigration;
+  startDrag(currentDragDeltaXY: Coordinate, healStack: boolean): void;
 
   /**
    * Execute a step of block dragging, based on the given event.  Update the
@@ -43,7 +45,7 @@ export interface IBlockDragger {
    * @param currentDragDeltaXY How far the pointer has moved from the position
    *     at the start of the drag, in pixel units.
    */
-  drag: AnyDuringMigration;
+  drag(e: Event, currentDragDeltaXY: Coordinate): void;
 
   /**
    * Finish a block drag and put the block back on the workspace.
@@ -51,15 +53,15 @@ export interface IBlockDragger {
    * @param currentDragDeltaXY How far the pointer has moved from the position
    *     at the start of the drag, in pixel units.
    */
-  endDrag: AnyDuringMigration;
+  endDrag(e: Event, currentDragDeltaXY: Coordinate): void;
 
   /**
    * Get a list of the insertion markers that currently exist.  Drags have 0, 1,
    * or 2 insertion markers.
    * @return A possibly empty list of insertion marker blocks.
    */
-  getInsertionMarkers: AnyDuringMigration;
+  getInsertionMarkers(): BlockSvg[];
 
   /** Sever all links from this object and do any necessary cleanup. */
-  dispose: () => void;
+  dispose(): void;
 }
diff --git a/core/interfaces/i_bounded_element.ts b/core/interfaces/i_bounded_element.ts
index f1fa6b77d..7e8f86627 100644
--- a/core/interfaces/i_bounded_element.ts
+++ b/core/interfaces/i_bounded_element.ts
@@ -13,6 +13,7 @@
  * @namespace Blockly.IBoundedElement
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {Rect} from '../utils/rect.js';
 goog.declareModuleId('Blockly.IBoundedElement');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -30,12 +31,12 @@ export interface IBoundedElement {
    * the element. Coordinate system: workspace coordinates.
    * @return Object with coordinates of the bounded element.
    */
-  getBoundingRectangle: AnyDuringMigration;
+  getBoundingRectangle(): Rect;
 
   /**
    * Move the element by a relative offset.
    * @param dx Horizontal offset in workspace units.
    * @param dy Vertical offset in workspace units.
    */
-  moveBy: AnyDuringMigration;
+  moveBy(dx: number, dy: number): void;
 }
diff --git a/core/interfaces/i_bubble.ts b/core/interfaces/i_bubble.ts
index 5701ab4b9..c846ef122 100644
--- a/core/interfaces/i_bubble.ts
+++ b/core/interfaces/i_bubble.ts
@@ -13,6 +13,8 @@
  * @namespace Blockly.IBubble
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {Coordinate} from '../utils/coordinate.js';
+import type {BlockDragSurfaceSvg} from '../block_drag_surface.js';
 goog.declareModuleId('Blockly.IBubble');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -36,13 +38,13 @@ export interface IBubble extends IDraggable, IContextMenu {
    * relative to the drawing surface's origin (0,0), in workspace units.
    * @return Object with .x and .y properties.
    */
-  getRelativeToSurfaceXY: AnyDuringMigration;
+  getRelativeToSurfaceXY(): Coordinate;
 
   /**
    * Return the root node of the bubble's SVG group.
    * @return The root SVG node of the bubble's group.
    */
-  getSvgRoot: AnyDuringMigration;
+  getSvgRoot(): SVGElement;
 
   /**
    * Set whether auto-layout of this bubble is enabled.  The first time a bubble
@@ -50,13 +52,13 @@ export interface IBubble extends IDraggable, IContextMenu {
    * dragged it to reposition, it renders where the user put it.
    * @param enable True if auto-layout should be enabled, false otherwise.
    */
-  setAutoLayout: AnyDuringMigration;
+  setAutoLayout(enable: boolean): void;
 
   /**
-   * Triggers a move callback if one exists at the end of a drag.
-   * @param adding True if adding, false if removing.
+   * Sets whether or not this bubble is being dragged.
+   * @param adding True if dragging, false otherwise.
    */
-  setDragging: AnyDuringMigration;
+  setDragging(dragging: boolean): void;
 
   /**
    * Move this bubble during a drag, taking into account whether or not there is
@@ -65,21 +67,22 @@ export interface IBubble extends IDraggable, IContextMenu {
    *     or null if no drag surface is in use.
    * @param newLoc The location to translate to, in workspace coordinates.
    */
-  moveDuringDrag: AnyDuringMigration;
+  moveDuringDrag(dragSurface: BlockDragSurfaceSvg|null, newLoc: Coordinate):
+      void;
 
   /**
    * Move the bubble to the specified location in workspace coordinates.
    * @param x The x position to move to.
    * @param y The y position to move to.
    */
-  moveTo: AnyDuringMigration;
+  moveTo(x: number, y: number): void;
 
   /**
    * Update the style of this bubble when it is dragged over a delete area.
    * @param enable True if the bubble is about to be deleted, false otherwise.
    */
-  setDeleteStyle: AnyDuringMigration;
+  setDeleteStyle(enable: boolean): void;
 
   /** Dispose of this bubble. */
-  dispose: () => void;
+  dispose(): void;
 }
diff --git a/core/interfaces/i_collapsible_toolbox_item.ts b/core/interfaces/i_collapsible_toolbox_item.ts
index 939b6597a..48a384aa1 100644
--- a/core/interfaces/i_collapsible_toolbox_item.ts
+++ b/core/interfaces/i_collapsible_toolbox_item.ts
@@ -21,6 +21,7 @@ goog.declareModuleId('Blockly.ICollapsibleToolboxItem');
 // import './i_toolbox_item.js';
 
 import type {ISelectableToolboxItem} from './i_selectable_toolbox_item.js';
+import type {IToolboxItem} from './i_toolbox_item.js';
 
 
 /**
@@ -32,15 +33,15 @@ export interface ICollapsibleToolboxItem extends ISelectableToolboxItem {
    * Gets any children toolbox items. (ex. Gets the subcategories)
    * @return The child toolbox items.
    */
-  getChildToolboxItems: AnyDuringMigration;
+  getChildToolboxItems(): IToolboxItem[];
 
   /**
    * Whether the toolbox item is expanded to show its child subcategories.
    * @return True if the toolbox item shows its children, false if it is
    *     collapsed.
    */
-  isExpanded: AnyDuringMigration;
+  isExpanded(): boolean;
 
   /** Toggles whether or not the toolbox item is expanded. */
-  toggleExpanded: () => void;
+  toggleExpanded(): void;
 }
diff --git a/core/interfaces/i_connection_checker.ts b/core/interfaces/i_connection_checker.ts
index 860c1f412..598d0f9dc 100644
--- a/core/interfaces/i_connection_checker.ts
+++ b/core/interfaces/i_connection_checker.ts
@@ -15,6 +15,8 @@
  * @namespace Blockly.IConnectionChecker
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {Connection} from '../connection.js';
+import type {RenderedConnection} from '../rendered_connection.js';
 goog.declareModuleId('Blockly.IConnectionChecker');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -40,7 +42,9 @@ export interface IConnectionChecker {
    *     drag checks.
    * @return Whether the connection is legal.
    */
-  canConnect: AnyDuringMigration;
+  canConnect(
+      a: Connection|null, b: Connection|null, isDragging: boolean,
+      opt_distance?: number): boolean;
 
   /**
    * Checks whether the current connection can connect with the target
@@ -53,7 +57,9 @@ export interface IConnectionChecker {
    * @return Connection.CAN_CONNECT if the connection is legal, an error code
    *     otherwise.
    */
-  canConnectWithReason: AnyDuringMigration;
+  canConnectWithReason(
+      a: Connection|null, b: Connection|null, isDragging: boolean,
+      opt_distance?: number): number;
 
   /**
    * Helper method that translates a connection error code into a string.
@@ -62,7 +68,8 @@ export interface IConnectionChecker {
    * @param b The second of the two connections being checked.
    * @return A developer-readable error string.
    */
-  getErrorMessage: AnyDuringMigration;
+  getErrorMessage(errorCode: number, a: Connection|null, b: Connection|null):
+      string;
 
   /**
    * Check that connecting the given connections is safe, meaning that it would
@@ -71,7 +78,7 @@ export interface IConnectionChecker {
    * @param b The second of the connections to check.
    * @return An enum with the reason this connection is safe or unsafe.
    */
-  doSafetyChecks: AnyDuringMigration;
+  doSafetyChecks(a: Connection|null, b: Connection|null): number;
 
   /**
    * Check whether this connection is compatible with another connection with
@@ -81,7 +88,7 @@ export interface IConnectionChecker {
    * @param b Connection to compare against.
    * @return True if the connections share a type.
    */
-  doTypeChecks: AnyDuringMigration;
+  doTypeChecks(a: Connection, b: Connection): boolean;
 
   /**
    * Check whether this connection can be made by dragging.
@@ -90,5 +97,6 @@ export interface IConnectionChecker {
    * @param distance The maximum allowable distance between connections.
    * @return True if the connection is allowed during a drag.
    */
-  doDragChecks: AnyDuringMigration;
+  doDragChecks(a: RenderedConnection, b: RenderedConnection, distance: number):
+      boolean;
 }
diff --git a/core/interfaces/i_contextmenu.ts b/core/interfaces/i_contextmenu.ts
index 983e9a78b..358290c50 100644
--- a/core/interfaces/i_contextmenu.ts
+++ b/core/interfaces/i_contextmenu.ts
@@ -22,5 +22,5 @@ export interface IContextMenu {
    * Show the context menu for this object.
    * @param e Mouse event.
    */
-  showContextMenu: AnyDuringMigration;
+  showContextMenu(e: Event): void;
 }
diff --git a/core/interfaces/i_copyable.ts b/core/interfaces/i_copyable.ts
index 21265f111..b44107560 100644
--- a/core/interfaces/i_copyable.ts
+++ b/core/interfaces/i_copyable.ts
@@ -26,14 +26,14 @@ export interface ICopyable extends ISelectable {
    * @return Copy metadata.
    * @internal
    */
-  toCopyData: AnyDuringMigration;
+  toCopyData(): CopyData|null;
 }
 
 export namespace ICopyable {
   export interface CopyData {
-    saveInfo: AnyDuringMigration|Element;
+    saveInfo: Object|Element;
     source: WorkspaceSvg;
-    typeCounts: AnyDuringMigration|null;
+    typeCounts: Object|null;
   }
 }
 
diff --git a/core/interfaces/i_deletable.ts b/core/interfaces/i_deletable.ts
index 599313d45..e0b1deaa4 100644
--- a/core/interfaces/i_deletable.ts
+++ b/core/interfaces/i_deletable.ts
@@ -25,5 +25,5 @@ export interface IDeletable {
    * Get whether this object is deletable or not.
    * @return True if deletable.
    */
-  isDeletable: AnyDuringMigration;
+  isDeletable(): boolean;
 }
diff --git a/core/interfaces/i_delete_area.ts b/core/interfaces/i_delete_area.ts
index 36304fd06..185552dbd 100644
--- a/core/interfaces/i_delete_area.ts
+++ b/core/interfaces/i_delete_area.ts
@@ -23,6 +23,7 @@ goog.declareModuleId('Blockly.IDeleteArea');
 // import './i_draggable.js';
 
 import type {IDragTarget} from './i_drag_target.js';
+import type {IDraggable} from './i_draggable.js';
 
 
 /**
@@ -41,5 +42,5 @@ export interface IDeleteArea extends IDragTarget {
    * @return Whether the element provided would be deleted if dropped on this
    *     area.
    */
-  wouldDelete: AnyDuringMigration;
+  wouldDelete(element: IDraggable, couldConnect: boolean): boolean;
 }
diff --git a/core/interfaces/i_drag_target.ts b/core/interfaces/i_drag_target.ts
index b743fd6d6..52c8aff0b 100644
--- a/core/interfaces/i_drag_target.ts
+++ b/core/interfaces/i_drag_target.ts
@@ -15,6 +15,10 @@
  * @namespace Blockly.IDragTarget
  */
 import * as goog from '../../closure/goog/goog.js';
+import {Rect} from '../utils/rect.js';
+
+import {IDraggable} from './i_draggable.js';
+
 goog.declareModuleId('Blockly.IDragTarget');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -40,33 +44,33 @@ export interface IDragTarget extends IComponent {
    * @return The component's bounding box. Null if drag target area should be
    *     ignored.
    */
-  getClientRect: AnyDuringMigration;
+  getClientRect(): Rect|null;
 
   /**
    * Handles when a cursor with a block or bubble enters this drag target.
    * @param dragElement The block or bubble currently being dragged.
    */
-  onDragEnter: AnyDuringMigration;
+  onDragEnter(dragElement: IDraggable): void;
 
   /**
    * Handles when a cursor with a block or bubble is dragged over this drag
    * target.
    * @param dragElement The block or bubble currently being dragged.
    */
-  onDragOver: AnyDuringMigration;
+  onDragOver(dragElement: IDraggable): void;
 
   /**
    * Handles when a cursor with a block or bubble exits this drag target.
    * @param dragElement The block or bubble currently being dragged.
    */
-  onDragExit: AnyDuringMigration;
+  onDragExit(dragElement: IDraggable): void;
 
   /**
    * Handles when a block or bubble is dropped on this component.
    * Should not handle delete here.
    * @param dragElement The block or bubble currently being dragged.
    */
-  onDrop: AnyDuringMigration;
+  onDrop(dragElement: IDraggable): void;
 
   /**
    * Returns whether the provided block or bubble should not be moved after
@@ -76,5 +80,5 @@ export interface IDragTarget extends IComponent {
    * @return Whether the block or bubble provided should be returned to drag
    *     start.
    */
-  shouldPreventMove: AnyDuringMigration;
+  shouldPreventMove(dragElement: IDraggable): boolean;
 }
diff --git a/core/interfaces/i_flyout.ts b/core/interfaces/i_flyout.ts
index 0976d7a5f..fac957fd8 100644
--- a/core/interfaces/i_flyout.ts
+++ b/core/interfaces/i_flyout.ts
@@ -29,7 +29,10 @@ goog.declareModuleId('Blockly.IFlyout');
 // import '../utils/svg.js';
 
 import type {WorkspaceSvg} from '../workspace_svg.js';
-
+import type {BlockSvg} from '../block_svg.js';
+import type {Coordinate} from '../utils/coordinate.js';
+import type {FlyoutDefinition} from '../utils/toolbox.js';
+import type {Svg} from '../utils/svg.js';
 import type {IRegistrable} from './i_registrable.js';
 
 
@@ -64,43 +67,43 @@ export interface IFlyout extends IRegistrable {
    *     or <g>.
    * @return The flyout's SVG group.
    */
-  createDom: AnyDuringMigration;
+  createDom(tagName: string|Svg<SVGSVGElement>|Svg<SVGGElement>): SVGElement;
 
   /**
    * Initializes the flyout.
    * @param targetWorkspace The workspace in which to create new blocks.
    */
-  init: AnyDuringMigration;
+  init(targetWorkspace: WorkspaceSvg): void;
 
   /**
    * Dispose of this flyout.
    * Unlink from all DOM elements to prevent memory leaks.
    */
-  dispose: () => void;
+  dispose(): void;
 
   /**
    * Get the width of the flyout.
    * @return The width of the flyout.
    */
-  getWidth: AnyDuringMigration;
+  getWidth(): number;
 
   /**
    * Get the height of the flyout.
-   * @return The width of the flyout.
+   * @return The height of the flyout.
    */
-  getHeight: AnyDuringMigration;
+  getHeight(): number;
 
   /**
    * Get the workspace inside the flyout.
    * @return The workspace inside the flyout.
    */
-  getWorkspace: AnyDuringMigration;
+  getWorkspace(): WorkspaceSvg;
 
   /**
    * Is the flyout visible?
    * @return True if visible.
    */
-  isVisible: AnyDuringMigration;
+  isVisible(): boolean;
 
   /**
    * Set whether the flyout is visible. A value of true does not necessarily
@@ -108,16 +111,16 @@ export interface IFlyout extends IRegistrable {
    * hidden.
    * @param visible True if visible.
    */
-  setVisible: AnyDuringMigration;
+  setVisible(visible: boolean): void;
 
   /**
    * Set whether this flyout's container is visible.
    * @param visible Whether the container is visible.
    */
-  setContainerVisible: AnyDuringMigration;
+  setContainerVisible(visible: boolean): void;
 
   /** Hide and empty the flyout. */
-  hide: () => void;
+  hide(): void;
 
   /**
    * Show and populate the flyout.
@@ -125,7 +128,7 @@ export interface IFlyout extends IRegistrable {
    *     of Nodes, a NodeList, a toolbox definition, or a string with the name
    *     of the dynamic category.
    */
-  show: AnyDuringMigration;
+  show(flyoutDef: FlyoutDefinition|string): void;
 
   /**
    * Create a copy of this block on the workspace.
@@ -133,31 +136,31 @@ export interface IFlyout extends IRegistrable {
    * @return The newly created block.
    * @throws {Error} if something went wrong with deserialization.
    */
-  createBlock: AnyDuringMigration;
+  createBlock(originalBlock: BlockSvg): BlockSvg;
 
   /** Reflow blocks and their mats. */
-  reflow: () => void;
+  reflow(): void;
 
   /**
    * @return True if this flyout may be scrolled with a scrollbar or by
    *     dragging.
    */
-  isScrollable: AnyDuringMigration;
+  isScrollable(): boolean;
 
   /**
    * Calculates the x coordinate for the flyout position.
    * @return X coordinate.
    */
-  getX: AnyDuringMigration;
+  getX(): number;
 
   /**
    * Calculates the y coordinate for the flyout position.
    * @return Y coordinate.
    */
-  getY: AnyDuringMigration;
+  getY(): number;
 
   /** Position the flyout. */
-  position: AnyDuringMigration;
+  position(): void;
 
   /**
    * Determine if a drag delta is toward the workspace, based on the position
@@ -167,7 +170,7 @@ export interface IFlyout extends IRegistrable {
    *     at mouse down, in pixel units.
    * @return True if the drag is toward the workspace.
    */
-  isDragTowardWorkspace: AnyDuringMigration;
+  isDragTowardWorkspace(currentDragDeltaXY: Coordinate): boolean;
 
   /**
    * Does this flyout allow you to create a new instance of the given block?
@@ -176,8 +179,8 @@ export interface IFlyout extends IRegistrable {
    * @return True if you can create a new instance of the block, false
    *     otherwise.
    */
-  isBlockCreatable: AnyDuringMigration;
+  isBlockCreatable(block: BlockSvg): boolean;
 
   /** Scroll the flyout to the beginning of its contents. */
-  scrollToStart: () => void;
+  scrollToStart(): void;
 }
diff --git a/core/interfaces/i_keyboard_accessible.ts b/core/interfaces/i_keyboard_accessible.ts
index 83ea432ae..327cf5d51 100644
--- a/core/interfaces/i_keyboard_accessible.ts
+++ b/core/interfaces/i_keyboard_accessible.ts
@@ -13,6 +13,7 @@
  * @namespace Blockly.IKeyboardAccessible
  */
 import * as goog from '../../closure/goog/goog.js';
+import {KeyboardShortcut} from '../shortcut_registry.js';
 goog.declareModuleId('Blockly.IKeyboardAccessible');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -30,5 +31,5 @@ export interface IKeyboardAccessible {
    * @param shortcut The shortcut to be handled.
    * @return True if the shortcut has been handled, false otherwise.
    */
-  onShortcut: AnyDuringMigration;
+  onShortcut(shortcut: KeyboardShortcut): boolean;
 }
diff --git a/core/interfaces/i_metrics_manager.ts b/core/interfaces/i_metrics_manager.ts
index 141982023..ea0d236c9 100644
--- a/core/interfaces/i_metrics_manager.ts
+++ b/core/interfaces/i_metrics_manager.ts
@@ -13,6 +13,9 @@
  * @namespace Blockly.IMetricsManager
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {ContainerRegion, ToolboxMetrics, AbsoluteMetrics, UiMetrics} from '../metrics_manager.js';
+import type {Size} from '../utils/size.js';
+import type {Metrics} from '../utils/metrics.js';
 goog.declareModuleId('Blockly.IMetricsManager');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -36,7 +39,7 @@ export interface IMetricsManager {
    * @return Whether the scroll area has fixed edges.
    * @internal
    */
-  hasFixedEdges: AnyDuringMigration;
+  hasFixedEdges(): boolean;
 
   /**
    * Returns the metrics for the scroll area of the workspace.
@@ -50,7 +53,9 @@ export interface IMetricsManager {
    *     again, if it is needed.
    * @return The metrics for the scroll container
    */
-  getScrollMetrics: AnyDuringMigration;
+  getScrollMetrics(
+      opt_getWorkspaceCoordinates?: boolean, opt_viewMetrics?: ContainerRegion,
+      opt_contentMetrics?: ContainerRegion): ContainerRegion;
 
   /**
    * Gets the width and the height of the flyout on the workspace in pixel
@@ -59,7 +64,7 @@ export interface IMetricsManager {
    * @param opt_own Whether to only return the workspace's own flyout.
    * @return The width and height of the flyout.
    */
-  getFlyoutMetrics: AnyDuringMigration;
+  getFlyoutMetrics(opt_own?: boolean): ToolboxMetrics;
 
   /**
    * Gets the width, height and position of the toolbox on the workspace in
@@ -69,14 +74,14 @@ export interface IMetricsManager {
    * simple toolbox @see {@link getFlyoutMetrics}.
    * @return The object with the width, height and position of the toolbox.
    */
-  getToolboxMetrics: AnyDuringMigration;
+  getToolboxMetrics(): ToolboxMetrics;
 
   /**
    * Gets the width and height of the workspace's parent SVG element in pixel
    * coordinates. This area includes the toolbox and the visible workspace area.
    * @return The width and height of the workspace's parent SVG element.
    */
-  getSvgMetrics: AnyDuringMigration;
+  getSvgMetrics(): Size;
 
   /**
    * Gets the absolute left and absolute top in pixel coordinates.
@@ -84,7 +89,7 @@ export interface IMetricsManager {
    * container.
    * @return The absolute metrics for the workspace.
    */
-  getAbsoluteMetrics: AnyDuringMigration;
+  getAbsoluteMetrics(): AbsoluteMetrics;
 
   /**
    * Gets the metrics for the visible workspace in either pixel or workspace
@@ -94,7 +99,7 @@ export interface IMetricsManager {
    * @return The width, height, top and left of the viewport in either workspace
    *     coordinates or pixel coordinates.
    */
-  getViewMetrics: AnyDuringMigration;
+  getViewMetrics(opt_getWorkspaceCoordinates?: boolean): ContainerRegion;
 
   /**
    * Gets content metrics in either pixel or workspace coordinates.
@@ -104,7 +109,7 @@ export interface IMetricsManager {
    *     workspace coordinates, false to get them in pixel coordinates.
    * @return The metrics for the content container.
    */
-  getContentMetrics: AnyDuringMigration;
+  getContentMetrics(opt_getWorkspaceCoordinates?: boolean): ContainerRegion;
 
   /**
    * Returns an object with all the metrics required to size scrollbars for a
@@ -136,11 +141,11 @@ export interface IMetricsManager {
    *     compare.
    * @return Contains size and position metrics of a top level workspace.
    */
-  getMetrics: AnyDuringMigration;
+  getMetrics(): Metrics;
 
   /**
    * Returns common metrics used by UI elements.
    * @return The UI metrics.
    */
-  getUiMetrics: AnyDuringMigration;
+  getUiMetrics(): UiMetrics;
 }
diff --git a/core/interfaces/i_movable.ts b/core/interfaces/i_movable.ts
index 6bc904941..8fd4ed58a 100644
--- a/core/interfaces/i_movable.ts
+++ b/core/interfaces/i_movable.ts
@@ -25,5 +25,5 @@ export interface IMovable {
    * Get whether this is movable or not.
    * @return True if movable.
    */
-  isMovable: AnyDuringMigration;
+  isMovable(): boolean;
 }
diff --git a/core/interfaces/i_positionable.ts b/core/interfaces/i_positionable.ts
index 1490f9cf4..40d770ae4 100644
--- a/core/interfaces/i_positionable.ts
+++ b/core/interfaces/i_positionable.ts
@@ -13,6 +13,8 @@
  * @namespace Blockly.IPositionable
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {Rect} from '../utils/rect.js';
+import type {UiMetrics} from '../metrics_manager.js';
 goog.declareModuleId('Blockly.IPositionable');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -36,7 +38,7 @@ export interface IPositionable extends IComponent {
    * @param metrics The workspace metrics.
    * @param savedPositions List of rectangles that are already on the workspace.
    */
-  position: AnyDuringMigration;
+  position(metrics: UiMetrics, savedPositions: Rect[]): void;
 
   /**
    * Returns the bounding rectangle of the UI element in pixel units relative to
@@ -44,5 +46,5 @@ export interface IPositionable extends IComponent {
    * @return The UI elements's bounding box. Null if bounding box should be
    *     ignored by other UI elements.
    */
-  getBoundingRectangle: AnyDuringMigration;
+  getBoundingRectangle(): Rect|null;
 }
diff --git a/core/interfaces/i_selectable.ts b/core/interfaces/i_selectable.ts
index 6fdaa8458..ef13bddcd 100644
--- a/core/interfaces/i_selectable.ts
+++ b/core/interfaces/i_selectable.ts
@@ -27,8 +27,8 @@ export interface ISelectable extends IDeletable, IMovable {
   id: string;
 
   /** Select this.  Highlight it visually. */
-  select: AnyDuringMigration;
+  select(): void;
 
   /** Unselect this.  Unhighlight it visually. */
-  unselect: AnyDuringMigration;
+  unselect(): void;
 }
diff --git a/core/interfaces/i_selectable_toolbox_item.ts b/core/interfaces/i_selectable_toolbox_item.ts
index 0cf663ae2..3fd8650a1 100644
--- a/core/interfaces/i_selectable_toolbox_item.ts
+++ b/core/interfaces/i_selectable_toolbox_item.ts
@@ -13,6 +13,7 @@
  * @namespace Blockly.ISelectableToolboxItem
  */
 import * as goog from '../../closure/goog/goog.js';
+import type {FlyoutItemInfoArray} from '../utils/toolbox';
 goog.declareModuleId('Blockly.ISelectableToolboxItem');
 
 /* eslint-disable-next-line no-unused-vars */
@@ -31,20 +32,20 @@ export interface ISelectableToolboxItem extends IToolboxItem {
    * Gets the name of the toolbox item. Used for emitting events.
    * @return The name of the toolbox item.
    */
-  getName: AnyDuringMigration;
+  getName(): string;
 
   /**
    * Gets the contents of the toolbox item. These are items that are meant to be
    * displayed in the flyout.
    * @return The definition of items to be displayed in the flyout.
    */
-  getContents: AnyDuringMigration;
+  getContents(): FlyoutItemInfoArray|string;
 
   /**
    * Sets the current toolbox item as selected.
    * @param _isSelected True if this category is selected, false otherwise.
    */
-  setSelected: AnyDuringMigration;
+  setSelected(_isSelected: boolean): void;
 
   /**
    * Gets the HTML element that is clickable.
@@ -53,11 +54,11 @@ export interface ISelectableToolboxItem extends IToolboxItem {
    * toolboxItem.
    * @return The HTML element that receives clicks.
    */
-  getClickTarget: AnyDuringMigration;
+  getClickTarget(): Element;
 
   /**
    * Handles when the toolbox item is clicked.
    * @param _e Click event to handle.
    */
-  onClick: AnyDuringMigration;
+  onClick(_e: Event): void;
 }
diff --git a/core/interfaces/i_serializer.ts b/core/interfaces/i_serializer.ts
index 5c926b86e..f48758254 100644
--- a/core/interfaces/i_serializer.ts
+++ b/core/interfaces/i_serializer.ts
@@ -43,7 +43,7 @@ export interface ISerializer {
    * @return A JS object containing the system's state, or null if there is no
    *     state to record.
    */
-  save(workspace: Workspace): AnyDuringMigration;
+  save(workspace: Workspace): Object|null;
   /* eslint-enable valid-jsdoc */
 
   /**
@@ -53,7 +53,7 @@ export interface ISerializer {
    * @param workspace The workspace the system to deserialize is associated
    *     with.
    */
-  load(state: AnyDuringMigration, workspace: Workspace): void;
+  load(state: Object, workspace: Workspace): void;
 
   /**
    * Clears the state of the plugin or system.
diff --git a/core/interfaces/i_styleable.ts b/core/interfaces/i_styleable.ts
index 292e18d56..12dde97b1 100644
--- a/core/interfaces/i_styleable.ts
+++ b/core/interfaces/i_styleable.ts
@@ -25,11 +25,11 @@ export interface IStyleable {
    * Adds a style on the toolbox. Usually used to change the cursor.
    * @param style The name of the class to add.
    */
-  addStyle: AnyDuringMigration;
+  addStyle(style: string): void;
 
   /**
    * Removes a style from the toolbox. Usually used to change the cursor.
    * @param style The name of the class to remove.
    */
-  removeStyle: AnyDuringMigration;
+  removeStyle(style: string): void;
 }
diff --git a/core/interfaces/i_toolbox.ts b/core/interfaces/i_toolbox.ts
index ceec06f30..2451ced6e 100644
--- a/core/interfaces/i_toolbox.ts
+++ b/core/interfaces/i_toolbox.ts
@@ -29,6 +29,10 @@ goog.declareModuleId('Blockly.IToolbox');
 // import '../workspace_svg.js';
 
 import type {IRegistrable} from './i_registrable.js';
+import type {IToolboxItem} from './i_toolbox_item.js';
+import type {ToolboxInfo} from '../utils/toolbox.js';
+import type {IFlyout} from './i_flyout.js';
+import type {WorkspaceSvg} from '../workspace_svg.js';
 
 
 /**
@@ -37,87 +41,87 @@ import type {IRegistrable} from './i_registrable.js';
  */
 export interface IToolbox extends IRegistrable {
   /** Initializes the toolbox. */
-  init: AnyDuringMigration;
+  init(): void;
 
   /**
    * Fills the toolbox with new toolbox items and removes any old contents.
    * @param toolboxDef Object holding information for creating a toolbox.
    */
-  render: AnyDuringMigration;
+  render(toolboxDef: ToolboxInfo): void;
 
   /**
    * Gets the width of the toolbox.
    * @return The width of the toolbox.
    */
-  getWidth: AnyDuringMigration;
+  getWidth(): number;
 
   /**
    * Gets the height of the toolbox.
-   * @return The width of the toolbox.
+   * @return The height of the toolbox.
    */
-  getHeight: AnyDuringMigration;
+  getHeight(): number;
 
   /**
    * Gets the toolbox flyout.
    * @return The toolbox flyout.
    */
-  getFlyout: AnyDuringMigration;
+  getFlyout(): IFlyout|null;
 
   /**
    * Gets the workspace for the toolbox.
    * @return The parent workspace for the toolbox.
    */
-  getWorkspace: AnyDuringMigration;
+  getWorkspace(): WorkspaceSvg;
 
   /**
    * Gets whether or not the toolbox is horizontal.
    * @return True if the toolbox is horizontal, false if the toolbox is
    *     vertical.
    */
-  isHorizontal: AnyDuringMigration;
+  isHorizontal(): boolean;
 
   /**
    * Positions the toolbox based on whether it is a horizontal toolbox and
    * whether the workspace is in rtl.
    */
-  position: AnyDuringMigration;
+  position(): void;
 
   /** Handles resizing the toolbox when a toolbox item resizes. */
-  handleToolboxItemResize: AnyDuringMigration;
+  handleToolboxItemResize(): void;
 
   /** Unhighlights any previously selected item. */
-  clearSelection: AnyDuringMigration;
+  clearSelection(): void;
 
   /**
    * Updates the category colours and background colour of selected categories.
    */
-  refreshTheme: AnyDuringMigration;
+  refreshTheme(): void;
 
   /**
    * Updates the flyout's content without closing it.  Should be used in
    * response to a change in one of the dynamic categories, such as variables or
    * procedures.
    */
-  refreshSelection: AnyDuringMigration;
+  refreshSelection(): void;
 
   /**
    * Sets the visibility of the toolbox.
    * @param isVisible True if toolbox should be visible.
    */
-  setVisible: AnyDuringMigration;
+  setVisible(isVisible: boolean): void;
 
   /**
    * Selects the toolbox item by it's position in the list of toolbox items.
    * @param position The position of the item to select.
    */
-  selectItemByPosition: AnyDuringMigration;
+  selectItemByPosition(position: number): void;
 
   /**
    * Gets the selected item.
    * @return The selected item, or null if no item is currently selected.
    */
-  getSelectedItem: AnyDuringMigration;
+  getSelectedItem(): IToolboxItem|null;
 
   /** Disposes of this toolbox. */
-  dispose: AnyDuringMigration;
+  dispose(): void;
 }
diff --git a/core/mutator.ts b/core/mutator.ts
index 1201e0630..881a382e2 100644
--- a/core/mutator.ts
+++ b/core/mutator.ts
@@ -319,7 +319,7 @@ export class Mutator extends Icon {
       const tree = this.workspace_!.options.languageTree;
       const flyout = this.workspace_!.getFlyout();
       if (tree) {
-        flyout!.init(this.workspace_);
+        flyout!.init(this.workspace_!);
         flyout!.show(tree);
       }
 
diff --git a/core/serialization/blocks.ts b/core/serialization/blocks.ts
index 5f2f03f77..7c27848ca 100644
--- a/core/serialization/blocks.ts
+++ b/core/serialization/blocks.ts
@@ -49,18 +49,18 @@ export interface ConnectionState {
  */
 export interface State {
   type: string;
-  id: string|undefined;
-  x: number|undefined;
-  y: number|undefined;
-  collapsed: boolean|undefined;
-  enabled: boolean|undefined;
-  inline: boolean|undefined;
-  data: string|undefined;
-  extraState: AnyDuringMigration|undefined;
-  icons: {[key: string]: AnyDuringMigration}|undefined;
-  fields: {[key: string]: AnyDuringMigration}|undefined;
-  inputs: {[key: string]: ConnectionState}|undefined;
-  next: ConnectionState|undefined;
+  id?: string;
+  x?: number;
+  y?: number;
+  collapsed?: boolean;
+  enabled?: boolean;
+  inline?: boolean;
+  data?: string;
+  extraState?: AnyDuringMigration;
+  icons?: {[key: string]: AnyDuringMigration};
+  fields?: {[key: string]: AnyDuringMigration};
+  inputs?: {[key: string]: ConnectionState};
+  next?: ConnectionState;
 }
 
 /**
diff --git a/core/shortcut_items.ts b/core/shortcut_items.ts
index dfdeb0f1c..a41f8069e 100644
--- a/core/shortcut_items.ts
+++ b/core/shortcut_items.ts
@@ -69,7 +69,8 @@ export function registerDelete() {
     name: names.DELETE,
     preconditionFn(workspace) {
       const selected = common.getSelected();
-      return !workspace.options.readOnly && selected && selected.isDeletable();
+      return !workspace.options.readOnly && selected != null &&
+          selected.isDeletable();
     },
     callback(workspace, e) {
       // Delete or backspace.
@@ -105,8 +106,8 @@ export function registerCopy() {
     name: names.COPY,
     preconditionFn(workspace) {
       const selected = common.getSelected();
-      return !workspace.options.readOnly && !Gesture.inProgress() && selected &&
-          selected.isDeletable() && selected.isMovable();
+      return !workspace.options.readOnly && !Gesture.inProgress() &&
+          selected != null && selected.isDeletable() && selected.isMovable();
     },
     callback(workspace, e) {
       // Prevent the default copy behavior, which may beep or otherwise indicate
@@ -139,10 +140,10 @@ export function registerCut() {
     name: names.CUT,
     preconditionFn(workspace) {
       const selected = common.getSelected();
-      return !!(
-          !workspace.options.readOnly && !Gesture.inProgress() && selected &&
-          selected instanceof BlockSvg && selected.isDeletable() &&
-          selected.isMovable() && !selected.workspace.isFlyout);
+      return !workspace.options.readOnly && !Gesture.inProgress() &&
+          selected != null && selected instanceof BlockSvg &&
+          selected.isDeletable() && selected.isMovable() &&
+          !selected.workspace!.isFlyout;
     },
     callback() {
       const selected = common.getSelected();
diff --git a/core/trashcan.ts b/core/trashcan.ts
index 5ecdbb74b..e764784ae 100644
--- a/core/trashcan.ts
+++ b/core/trashcan.ts
@@ -42,6 +42,7 @@ import * as dom from './utils/dom.js';
 import {Rect} from './utils/rect.js';
 import {Size} from './utils/size.js';
 import {Svg} from './utils/svg.js';
+import {BlockInfo} from './utils/toolbox.js';
 import * as toolbox from './utils/toolbox.js';
 import type {WorkspaceSvg} from './workspace_svg.js';
 
@@ -67,9 +68,7 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
    * The trashcan flyout.
    * @internal
    */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'IFlyout'.
-  flyout: IFlyout = null as AnyDuringMigration;
+  flyout: IFlyout|null = null;
 
   /** Current open/close state of the lid. */
   isLidOpen = false;
@@ -81,17 +80,13 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
   private minOpenness_ = 0;
 
   /** The SVG group containing the trash can. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGElement'.
-  private svgGroup_: SVGElement = null as AnyDuringMigration;
+  private svgGroup_: SVGElement|null = null;
 
   /** The SVG image element of the trash can lid. */
-  // AnyDuringMigration because:  Type 'null' is not assignable to type
-  // 'SVGElement'.
-  private svgLid_: SVGElement = null as AnyDuringMigration;
+  private svgLid_: SVGElement|null = null;
 
   /** Task ID of opening/closing animation. */
-  private lidTask_: AnyDuringMigration = 0;
+  private lidTask_: ReturnType<typeof setTimeout>|null = null;
 
   /** Current state of lid opening (0.0 = closed, 1.0 = open). */
   private lidOpen_ = 0;
@@ -222,8 +217,8 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
   init() {
     if (this.workspace.options.maxTrashcanContents > 0) {
       dom.insertAfter(
-          this.flyout.createDom(Svg.SVG), this.workspace.getParentSvg());
-      this.flyout.init(this.workspace);
+          this.flyout?.createDom(Svg.SVG)!, this.workspace.getParentSvg());
+      this.flyout?.init(this.workspace);
     }
     this.workspace.getComponentManager().addComponent({
       component: this,
@@ -248,17 +243,12 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     this.workspace.getComponentManager().removeComponent('trashcan');
     if (this.svgGroup_) {
       dom.removeNode(this.svgGroup_);
-      // AnyDuringMigration because:  Type 'null' is not assignable to type
-      // 'SVGElement'.
-      this.svgGroup_ = null as AnyDuringMigration;
+      this.svgGroup_ = null;
+    }
+    this.svgLid_ = null;
+    if (this.lidTask_) {
+      clearTimeout(this.lidTask_);
     }
-    // AnyDuringMigration because:  Type 'null' is not assignable to type
-    // 'SVGElement'.
-    this.svgLid_ = null as AnyDuringMigration;
-    // AnyDuringMigration because:  Type 'null' is not assignable to type
-    // 'WorkspaceSvg'.
-    this.workspace = null as AnyDuringMigration;
-    clearTimeout(this.lidTask_);
   }
 
   /**
@@ -285,7 +275,7 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     const contents = this.contents_.map(function(string) {
       return JSON.parse(string);
     });
-    this.flyout.show(contents);
+    this.flyout?.show(contents);
     this.fireUiEvent_(true);
   }
 
@@ -294,7 +284,7 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     if (!this.contentsIsOpen()) {
       return;
     }
-    this.flyout.hide();
+    this.flyout?.hide();
     this.fireUiEvent_(false);
     this.workspace.recordDragTargets();
   }
@@ -355,7 +345,7 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
 
     this.top_ = positionRect.top;
     this.left_ = positionRect.left;
-    this.svgGroup_.setAttribute(
+    this.svgGroup_?.setAttribute(
         'transform', 'translate(' + this.left_ + ',' + this.top_ + ')');
   }
 
@@ -425,7 +415,9 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     if (this.isLidOpen === state) {
       return;
     }
-    clearTimeout(this.lidTask_);
+    if (this.lidTask_) {
+      clearTimeout(this.lidTask_);
+    }
     this.isLidOpen = state;
     this.animateLid_();
   }
@@ -442,9 +434,9 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
 
     // Linear interpolation between min and max.
     const opacity = OPACITY_MIN + this.lidOpen_ * (OPACITY_MAX - OPACITY_MIN);
-    // AnyDuringMigration because:  Type 'number' is not assignable to type
-    // 'string'.
-    this.svgGroup_.style.opacity = opacity as AnyDuringMigration;
+    if (this.svgGroup_) {
+      this.svgGroup_.style.opacity = opacity.toString();
+    }
 
     if (this.lidOpen_ > this.minOpenness_ && this.lidOpen_ < 1) {
       this.lidTask_ =
@@ -460,7 +452,7 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     const openAtRight =
         this.workspace.toolboxPosition === toolbox.Position.RIGHT ||
         this.workspace.horizontalLayout && this.workspace.RTL;
-    this.svgLid_.setAttribute(
+    this.svgLid_?.setAttribute(
         'transform',
         'rotate(' + (openAtRight ? -lidAngle : lidAngle) + ',' +
             (openAtRight ? 4 : WIDTH - 4) + ',' + (LID_HEIGHT - 2) + ')');
@@ -547,7 +539,8 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
     }
     const deleteEvent = event as BlockDelete;
     if (event.type === eventUtils.BLOCK_DELETE && !deleteEvent.wasShadow) {
-      const cleanedJson = this.cleanBlockJson_(deleteEvent.oldJson);
+      const cleanedJson =
+          JSON.stringify(this.cleanBlockJson_(deleteEvent.oldJson));
       if (this.contents_.indexOf(cleanedJson) !== -1) {
         return;
       }
@@ -565,9 +558,10 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
    * Converts JSON representing a block into text that can be stored in the
    * content array.
    * @param json A JSON representation of a block's state.
-   * @return Text representing the JSON, cleaned of all unnecessary attributes.
+   * @return A BlockInfo object corresponding to the JSON, cleaned of all
+   *     unnecessary attributes.
    */
-  private cleanBlockJson_(json: blocks.State): string {
+  private cleanBlockJson_(json: blocks.State): BlockInfo {
     // Create a deep copy.
     json = JSON.parse(JSON.stringify(json)) as blocks.State;
 
@@ -595,30 +589,39 @@ export class Trashcan extends DeleteArea implements IAutoHideable,
       const inputs = json['inputs'];
       for (const name in inputs) {
         const input = inputs[name];
-        // AnyDuringMigration because:  Argument of type 'State | undefined' is
-        // not assignable to parameter of type 'State'.
-        cleanRec((input as AnyDuringMigration)['block']);
-        // AnyDuringMigration because:  Argument of type 'State | undefined' is
-        // not assignable to parameter of type 'State'.
-        cleanRec((input as AnyDuringMigration)['shadow']);
+        const block = input['block'];
+        const shadow = input['shadow'];
+        if (block) {
+          cleanRec(block);
+        }
+        if (shadow) {
+          cleanRec(shadow);
+        }
       }
       if (json['next']) {
         const next = json['next'];
-        // AnyDuringMigration because:  Argument of type 'State | undefined' is
-        // not assignable to parameter of type 'State'.
-        cleanRec((next as AnyDuringMigration)['block']);
-        // AnyDuringMigration because:  Argument of type 'State | undefined' is
-        // not assignable to parameter of type 'State'.
-        cleanRec((next as AnyDuringMigration)['shadow']);
+        const block = next['block'];
+        const shadow = next['shadow'];
+        if (block) {
+          cleanRec(block);
+        }
+        if (shadow) {
+          cleanRec(shadow);
+        }
       }
     }
 
     cleanRec(json);
-    (json as AnyDuringMigration)['kind'] = 'BLOCK';
-    return JSON.stringify(json);
+
+    const blockInfo: BlockInfo = {
+      'kind': 'BLOCK',
+      ...json,
+    };
+    return blockInfo;
   }
 }
 
+
 /** Width of both the trash can and lid images. */
 const WIDTH = 47;
 
diff --git a/core/utils/toolbox.ts b/core/utils/toolbox.ts
index 5f8cbb1a5..f9c9fe1fa 100644
--- a/core/utils/toolbox.ts
+++ b/core/utils/toolbox.ts
@@ -36,22 +36,22 @@ import * as userAgent from './useragent.js';
  */
 export interface BlockInfo {
   kind: string;
-  blockxml: string|Node|undefined;
-  type: string|undefined;
-  gap: string|number|undefined;
-  disabled: string|boolean|undefined;
-  enabled: boolean|undefined;
-  id: string|undefined;
-  x: number|undefined;
-  y: number|undefined;
-  collapsed: boolean|undefined;
-  inline: boolean|undefined;
-  data: string|undefined;
-  extraState: AnyDuringMigration|undefined;
-  icons: {[key: string]: AnyDuringMigration}|undefined;
-  fields: {[key: string]: AnyDuringMigration}|undefined;
-  inputs: {[key: string]: ConnectionState}|undefined;
-  next: ConnectionState|undefined;
+  blockxml?: string|Node;
+  type?: string;
+  gap?: string|number;
+  disabled?: string|boolean;
+  enabled?: boolean;
+  id?: string;
+  x?: number;
+  y?: number;
+  collapsed?: boolean;
+  inline?: boolean;
+  data?: string;
+  extraState?: AnyDuringMigration;
+  icons?: {[key: string]: AnyDuringMigration};
+  fields?: {[key: string]: AnyDuringMigration};
+  inputs?: {[key: string]: ConnectionState};
+  next?: ConnectionState;
 }
 
 /**
diff --git a/core/workspace_svg.ts b/core/workspace_svg.ts
index 375141602..032835e88 100644
--- a/core/workspace_svg.ts
+++ b/core/workspace_svg.ts
@@ -895,7 +895,6 @@ export class WorkspaceSvg extends Workspace implements IASTNodeLocationSvg {
     }
 
     if (this.grid_) {
-      this.grid_.dispose();
       // AnyDuringMigration because:  Type 'null' is not assignable to type
       // 'Grid'.
       this.grid_ = null as AnyDuringMigration;