update docs against 5678

Signed-off-by: Nwusongqing <wusongqing@huawei.com>

en/application-dev/reference/apis/js-apis-backgroundTaskManager.md

-# Background Task Management
+# BackgroundTaskManager
 
-> ![icon-note.gif](public_sys-resources/icon-note.gif) **NOTE**
+This module provides background task management.
+
+If a service needs to be continued when the application or service module is running in the background (not visible to users), the application or service module can request a transient task or continuous task for delayed suspension based on the service type.
+
+If an application has a task that needs to be continued when the application is switched to the background and can be completed within a short period of time, the application can request a transient task. For example, if a user chooses to clear junk files in the **Files** application and exits the application, the application can request a transient task to complete the cleanup.
+
+If an application has a service that can be intuitively perceived by users and needs to run in the background for a long period of time (for example, music playback in the background), the application can request a continuous task.
+
+> **NOTE**
 >
 > The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.
 
@@ -26,7 +34,7 @@ The default duration of delayed suspension is 180000 when the battery level is h
 | Name     | Type                  | Mandatory  | Description                            |
 | -------- | -------------------- | ---- | ------------------------------ |
 | reason   | string               | Yes   | Reason for delayed transition to the suspended state.                    |
-| callback | Callback<void> | Yes   | Invoked when a delay is about to time out. Generally, this callback is used to notify the application 6 seconds before the delay times out. |
+| callback | Callback<void> | Yes   | Invoked when a delay is about to time out. Generally, this callback is used to notify the application 6 seconds before the delay times out.|
 
 **Return value**
 | Type                                   | Description       |
@@ -191,12 +199,12 @@ Requests a continuous task from the system. This API uses a promise to return th
 | --------- | ---------------------------------- | ---- | ----------------------- |
 | context   | [Context](js-apis-Context.md)      | Yes   | Application context.              |
 | bgMode    | [BackgroundMode](#backgroundmode8) | Yes   | Background mode requested.            |
-| wantAgent | [WantAgent](js-apis-wantAgent.md)  | Yes    | Notification parameter, which is used to specify the target page that is redirected to when a continuous task notification is clicked. |
+| wantAgent | [WantAgent](js-apis-wantAgent.md)  | Yes   | Notification parameter, which is used to specify the target page that is redirected to when a continuous task notification is clicked.|
 
 **Return value**
 | Type            | Description              |
 | -------------- | ---------------- |
-| Promise\<void> | Promise used to return the result. |
+| Promise\<void> | Promise used to return the result.|
 
 **Example**
 ```js
@@ -239,7 +247,7 @@ Requests to cancel a continuous task. This API uses an asynchronous callback to
 | Name     | Type                           | Mandatory  | Description                    |
 | -------- | ----------------------------- | ---- | ---------------------- |
 | context  | [Context](js-apis-Context.md) | Yes   | Application context.             |
-| callback | AsyncCallback&lt;void&gt;     | Yes    | Callback used to return the result. |
+| callback | AsyncCallback&lt;void&gt;     | Yes   | Callback used to return the result.|
 
 **Example**
 ```js
@@ -269,12 +277,12 @@ Requests to cancel a continuous task. This API uses a promise to return the resu
 **Parameters**
 | Name    | Type                           | Mandatory  | Description       |
 | ------- | ----------------------------- | ---- | --------- |
-| context | [Context](js-apis-Context.md) | Yes    | Application context. |
+| context | [Context](js-apis-Context.md) | Yes   | Application context.|
 
 **Return value**
 | Type            | Description              |
 | -------------- | ---------------- |
-| Promise\<void> | Promise used to return the result. |
+| Promise\<void> | Promise used to return the result.|
 
 **Example**
 ```js