update docs

Signed-off-by: NAnnie_wang <annie.wangli@huawei.com>

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

+# Standard NFC Tag Session
+
+The **tagSession** module provides common APIs for establishing connections and transferring data.
+
+> **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.
+
+## **Modules to Import**
+
+```js
+import tag from '@ohos.nfc.tag';
+```
+
+## tagSession
+
+Provides common APIs for establishing connections and transferring data. **tagSession** is the base class of all [NFC tag technologies](js-apis-nfctech.md).
+
+A child class instance is required to access the following interfaces. You can use **get**XX**Tag()** to obtain a child class instance.
+
+The specific method varies with the NFC tag technology in use. For details, see [nfcTag](js-apis-nfcTag.md).
+
+### tagSession.connectTag
+
+connectTag(): boolean;
+
+Connects to this tag.
+
+Call this method to set up a connection before reading data from or writing data to a tag.
+
+**Required permissions**: ohos.permission.NFC_TAG
+
+**System capability**: SystemCapability.Communication.NFC.Core
+
+**Return value**
+
+| **Type**| **Description**                            |
+| ------------------ | --------------------------|
+| boolean  | Returns **true** if the operation is successful; returns **false** otherwise.|
+
+**Example**
+
+```js
+import tag from '@ohos.nfc.tag';
+
+// tagInfo is an object given by the NFC service when a tag is dispatched.
+let isNfcConnected = tag.getXXXTag(taginfo).connectTag(); 
+console.log("isNfcConnected:" +isNfcConnected);
+```
+
+### tagSession.reset()
+
+reset(): void
+
+Resets the connection to this tag and restores the default timeout duration for writing data to the tag.
+
+**Required permissions**: ohos.permission.NFC_TAG
+
+**System capability**: SystemCapability.Communication.NFC.Core
+
+**Return value**
+
+| **Type**| **Description**                            |
+| ------------------ | --------------------------|
+| boolean  | Returns **true** if the operation is successful; returns **false** otherwise.|
+
+**Example**
+
+```js
+import tag from '@ohos.nfc.tag';
+
+// tagInfo is an object given by the NFC service when a tag is dispatched.
+let reset = tag.getXXXTag(taginfo).reset(); 
+console.log("reset:" +reset);
+```
+
+### tagSession.isTagConnected
+
+isTagConnected(): boolean
+
+Checks whether the tag is connected.
+
+**Required permissions**: ohos.permission.NFC_TAG
+
+**System capability**: SystemCapability.Communication.NFC.Core
+
+**Return value**
+
+| **Type**| **Description**                            |
+| ------------------ | --------------------------|
+| boolean  | Returns **true** if the tag is connected; returns **false** otherwise.|
+
+**Example**
+
+```js
+import tag from '@ohos.nfc.tag';
+
+// tagInfo is an Object given by nfc service when tag is dispatched.
+let isTagConnected = tag.getXXXTag(taginfo).isTagConnected(); 
+console.log("isTagConnected:" +isTagConnected);
+```
+
+### tagSession.getMaxSendLength
+
+getMaxSendLength(): number
+
+Obtains the maximum length of the data that can be sent to the tag.
+
+**Required permissions**: ohos.permission.NFC_TAG
+
+**System capability**: SystemCapability.Communication.NFC.Core
+
+**Return value**
+
+| **Type**| **Description**                            |
+| ------------------ | --------------------------|
+| number  | Maximum data length obtained.|
+
+**Example**
+
+```js
+import tag from '@ohos.nfc.tag';
+
+// tagInfo is an object given by the NFC service when a tag is dispatched.
+let mazSendLen = tag.getXXXTag(taginfo).getMaxSendLength(); 
+console.log("mazSendLen:" +mazSendLen);
+```