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Signed-off-by: Nester.zhou <ester.zhou@huawei.com>

en/application-dev/application-models/accessibilityextensionability.md

+# AccessibilityExtensionAbility Development
+
+The **AccessibilityExtensionAbility** module provides accessibility extension capabilities based on the **ExtensionAbility** framework. You can develop your accessibility applications by applying the **AccessibilityExtensionAbility** template to enhance usability.
+
+> **Environment Requirements**
+>
+> IDE: DevEco Studio 3.0 Beta3 (3.0.0.900) or later
+>
+> SDK: API version 9 or later
+>
+> Model: stage
+
+This document is organized as follows:
+
+- [Creating an AccessibilityExtAbility File](#creating-an-accessibility-extension-service)
+- [Processing an Accessibility Event](#processing-an-accessibility-event)
+- [Declaring Capabilities of Accessibility Extension Services](#declaring-capabilities-of-accessibility-extension-services)
+- [Enabling a Custom Accessibility Extension Service](#enabling-a-custom-accessibility-extension-service)
+
+## Creating an Accessibility Extension Service
+
+You can create an accessibility extension service by creating a project from scratch or adding the service to an existing project.
+
+### Creating a Project
+
+Perform the following steps in DevEco Studio:
+1. From the upper left corner of DevEco Studio, choose **File** > **New** > **Create Project**.
+2. By following the project creation wizard, click the **OpenHarmony** tab, select the **Empty Ability** template, and then click **Next**.
+3. Set **Project type** to **Application**, **Compile API** (or **Compile SDK**, depending on the version used) to **9**, and **Model** to **Stage**, and then click **Finish**.
+
+### Creating an AccessibilityExtAbility File
+
+To add an accessibility extension service to a project, create the **AccessibilityExtAbility** folder in the **ets** folder of the project, create the **AccessibilityExtAbility.ts** file in the new folder, and add the following code to the new file:
+
+```typescript
+import AccessibilityExtensionAbility from '@ohos.application.AccessibilityExtensionAbility';
+
+class AccessibilityExtAbility extends AccessibilityExtensionAbility {
+    onConnect() {
+        console.log('AccessibilityExtAbility onConnect');
+    }
+
+    onDisconnect() {
+        console.log('AccessibilityExtAbility onDisconnect');
+    }
+
+    onAccessibilityEvent(accessibilityEvent) {
+        console.log('AccessibilityExtAbility onAccessibilityEvent: ' + JSON.stringify(accessibilityEvent));
+    }
+}
+
+export default AccessibilityExtAbility;
+```
+
+The APIs defined in the file are as follows.
+
+| API| Description|
+| ---- | ---- |
+| onConnect(): void | Called when a connection with the extension service is set up.|
+| onDisconnect(): void | Called when the connection with the extension service is severed.|
+| onAccessibilityEvent(event: AccessibilityEvent): void | Called when an accessibility event occurs|
+
+## Processing an Accessibility Event
+
+You can process the service logic for accessibility events in the **onAccessibilityEvent()** API. For details about the events, see [AccessibilityEvent](../reference/apis/js-apis-application-accessibilityExtensionAbility.md#accessibilityevent). The following code snippet uses the **pageStateUpdate** event as an example.
+
+```typescript
+onAccessibilityEvent(accessibilityEvent) {
+    console.log('AccessibilityExtAbility onAccessibilityEvent: ' + JSON.stringify(accessibilityEvent));
+    if (accessibilityEvent.eventType === 'pageStateUpdate') {
+        console.log('AccessibilityExtAbility onAccessibilityEvent: pageStateUpdate');
+        // TODO: Develop custom logic.
+    }
+}
+```
+For an accessibility event, you can use the APIs of the [AccessibilityExtensionContext](../reference/apis/js-apis-inner-application-accessibilityExtensionContext.md) module to configure the concerned information, obtain root information, and inject gestures.
+
+You can also process physical key events in the accessibility extension service. For details, see [onKeyEvent](../reference/apis/js-apis-application-accessibilityExtensionAbility.md#accessibilityextensionabilityonkeyevent).
+
+## Declaring Capabilities of Accessibility Extension Services
+
+After developing the custom logic for an accessibility extension service, you must add the configuration information of the service to the corresponding module-level **module.json5** file in the project directory. In the file, the **srcEntrance** tag indicates the path to the accessibility extension service. Make sure the value of the **type** tag is fixed at **accessibility**. Otherwise, the connection to the service will fail.
+
+```json
+"extensionAbilities": [
+  {
+    "name": "AccessibilityExtAbility",
+    "srcEntrance": "./ets/AccessibilityExtAbility/AccessibilityExtAbility.ts",
+    "label": "$string:MainAbility_label",
+    "description": "$string:MainAbility_desc",
+    "type": "accessibility",
+    "metadata": [
+      {
+        "name": "ohos.accessibleability",
+        "resource": "$profile:accessibility_config"
+      }
+    ]
+  }
+]
+```
+**accessibility_config** is the specific configuration of the accessibility extension service. You need to create the **accessibility_config.json** file in **resources/base/profile/** and declare the [capabilities](../reference/apis/js-apis-accessibility.md#capability) of the service in the file.
+```json
+{
+  "accessibilityCapabilities": [
+    "retrieve",
+    "gesture"
+  ]
+}
+```
+## Enabling a Custom Accessibility Extension Service
+
+To enable or disable an accessibility extension service, run the following command:
+- To enable the service: **accessibility enable -a AccessibilityExtAbility -b com.example.demo -c rg**
+- To disable the service: **accessibility disable -a AccessibilityExtAbility -b com.example.demo**
+
+In the preceding commands, **AccessibilityExtAbility** indicates the name of the accessibility extension service, **com.example.demo** indicates the bundle name, and **rg** indicates the capabilities (**r** is short for retrieve).
+
+If the service is enabled or disabled successfully, the message "enable ability successfully" or "disable ability successfully" is displayed.