diff --git a/web/src/engine/src/keyboard/index.ts b/web/src/engine/src/keyboard/index.ts
index c8ea67593f..0e8fc53d3e 100644
--- a/web/src/engine/src/keyboard/index.ts
+++ b/web/src/engine/src/keyboard/index.ts
@@ -4,7 +4,7 @@ export { JSKeyboard, LayoutState } from "./keyboards/jsKeyboard.js";
 export { KeyboardMinimalInterface } from './keyboards/keyboardMinimalInterface.js';
 export { KMXKeyboard } from './keyboards/kmxKeyboard.js';
 export { KeyboardHarness, KeyboardKeymanGlobal, MinimalCodesInterface, MinimalKeymanGlobal } from "./keyboards/keyboardHarness.js";
-export { Keyboard, KeyboardLoaderBase } from "./keyboards/keyboardLoaderBase.js";
+export { NotifyEventCode, Keyboard, KeyboardLoaderBase } from "./keyboards/keyboardLoaderBase.js";
 export { KeyboardLoadErrorBuilder, KeyboardMissingError, KeyboardScriptError, KeyboardDownloadError, InvalidKeyboardError } from './keyboards/keyboardLoadError.js'
 export { BeepHandler, EventMap, KeyboardProcessor } from "./keyboards/keyboardProcessor.js";
 export {
diff --git a/web/src/engine/src/keyboard/keyboards/jsKeyboard.ts b/web/src/engine/src/keyboard/keyboards/jsKeyboard.ts
index 90b45f3ba5..5fd6e06530 100644
--- a/web/src/engine/src/keyboard/keyboards/jsKeyboard.ts
+++ b/web/src/engine/src/keyboard/keyboards/jsKeyboard.ts
@@ -14,6 +14,7 @@ type TouchLayoutSpec = TouchLayout.TouchLayoutPlatform & { isDefault?: boolean};
 
 import { Version, DeviceSpec } from "keyman/common/web-utils";
 import { StateKeyMap } from "./stateKeyMap.js";
+import { NotifyEventCode } from './keyboardLoaderBase.js';
 
 /**
  * Stores preprocessed properties of a keyboard for quick retrieval later.
@@ -356,11 +357,12 @@ export class JSKeyboard {
   /**
    * Notifies keyboard of keystroke or other event
    *
-   * @param       {number}    command     event code (16,17,18) or 0
-   * @param       {TextStore} textStore   textStore
-   * @param       {number}    data        1 or 0
+   * @param       {NotifyEventCode}  command     event code (16,17,18) or 0
+   * @param       {TextStore}        textStore   textStore
+   * @param       {number}           data        1 for KeyDown or FocusReceived,
+   *                                             0 for KeyUp or FocusLost
    */
-  public notify(command: number, textStore: TextStore, data: number): void { // I2187
+  public notify(command: NotifyEventCode, textStore: TextStore, data: number): void { // I2187
     // Good example use case - the Japanese CJK-picker keyboard
     if(typeof(this.scriptObject['KNS']) == 'function') {
       this.scriptObject['KNS'](command, textStore, data);
diff --git a/web/src/engine/src/keyboard/keyboards/keyboardLoaderBase.ts b/web/src/engine/src/keyboard/keyboards/keyboardLoaderBase.ts
index b7fe16dd1d..2d938e159e 100644
--- a/web/src/engine/src/keyboard/keyboards/keyboardLoaderBase.ts
+++ b/web/src/engine/src/keyboard/keyboards/keyboardLoaderBase.ts
@@ -4,6 +4,14 @@ import { KMXKeyboard } from './kmxKeyboard.js';
 import { KeyboardHarness } from "./keyboardHarness.js";
 import KeyboardProperties from "./keyboardProperties.js";
 import { KeyboardLoadErrorBuilder, StubBasedErrorBuilder, UriBasedErrorBuilder } from './keyboardLoadError.js';
+import { Codes } from '../codes.js';
+
+export enum NotifyEventCode {
+  FocusEvent = 0,
+  ShiftKey = Codes.keyCodes.K_SHIFT,
+  ControlKey = Codes.keyCodes.K_CONTROL,
+  AltKey = Codes.keyCodes.K_ALT,
+};
 
 export type KeyboardStub = KeyboardProperties & { filename: string };
 export type Keyboard = JSKeyboard | KMXKeyboard;
diff --git a/web/src/engine/src/keyboard/keyboards/kmxKeyboard.ts b/web/src/engine/src/keyboard/keyboards/kmxKeyboard.ts
index 73b62558dc..1c8123192f 100644
--- a/web/src/engine/src/keyboard/keyboards/kmxKeyboard.ts
+++ b/web/src/engine/src/keyboard/keyboards/kmxKeyboard.ts
@@ -7,6 +7,7 @@ import { ActiveKey, ActiveSubKey } from './activeLayout.js';
 import { StateKeyMap } from './stateKeyMap.js';
 import { KeyEvent } from '../keyEvent.js';
 import { TextStore } from '../textStore.js';
+import { NotifyEventCode } from './keyboardLoaderBase.js';
 
 /**
  * Acts as a wrapper class for KMX(+) Keyman keyboards
@@ -99,12 +100,15 @@ export class KMXKeyboard {
   }
 
   /**
-   * @param       {number}    eventCode     event code (16,17,18) or 0 // TODO-web-core: document meaning of these! (#15290)
-   * @param       {TextStore} textStore     textStore
-   * @param       {number}    data          1 or 0
    * Notifies keyboard of keystroke or other event
+   *
+   * @param       {NotifyEventCode}  eventCode     key code (16-18: Shift, Control or Alt),
+   *                                               or 0 for focus
+   * @param       {TextStore}        textStore     textStore
+   * @param       {number}           data          1 for KeyDown or FocusReceived,
+   *                                               0 for KeyUp or FocusLost
    */
-  public notify(eventCode: 16|17|18|0, textStore: TextStore, data: number) { // I2187
+  public notify(eventCode: NotifyEventCode, textStore: TextStore, data: number): void { // I2187
     // TODO-web-core: do we need to support this? (#15290)
   }