Update metadata_xls.md

- Added Salomé's additions

Author: AmandaJ-W

source/metadata_xls.md

@@ -34,11 +34,12 @@ Available metadata questions in XLSForm include:
 | end | Records the date and time when a submission is finalized. |
 | today | Records the date of the submission. |
 | deviceid | Records the unique identification of the device or browser used to collect data. The <code>deviceid</code> is automatically generated and cannot be modified by users.<br><br>**Note:** In KoboCollect, the <code>deviceid</code> is updated whenever the app is reinstalled on a device. In Enketo, the <code>deviceid</code> resets any time a new browser window is used. |
-| username | In KoboCollect, records the username saved in the <a href="https://support.kobotoolbox.org/kobocollect_settings.html#user-and-device-identity-settings">KoboCollect app settings</a>. If no username is set, it records the one used to sign in to the server.<br>In Enketo, records the account username only if <a href="https://support.kobotoolbox.org/project_sharing_settings.html#allowing-submissions-without-authentication">authentication is required</a>. |
+| username | In KoboCollect, records the username saved in the <a href="https://support.kobotoolbox.org/kobocollect_settings.html#user-and-device-identity-settings">KoboCollect app settings</a>. If no username is set, it records the one used to sign in to the server.<br>In Enketo, records the account username only if <a href="https://support.kobotoolbox.org/project_sharing_settings.html#allowing-submissions-without-authentication">authentication is required</a>.<br><br>**Note:** Because the `username` field can be edited in KoboCollect, it may not match the account used to authenticate to the server. To see which account submitted the data, refer to the automatically generated `_submitted_by` field.|
 | phonenumber | Records the phone number stored in the <a href="https://support.kobotoolbox.org/kobocollect_settings.html#user-and-device-identity-settings">KoboCollect app settings</a>. This metadata question is not supported in Enketo. |
 | email | Records the email address from the <a href="https://support.kobotoolbox.org/kobocollect_settings.html#user-and-device-identity-settings">KoboCollect app settings</a>. This metadata question is not supported in Enketo. |
-| start-geopoint | Captures GPS coordinates when the form is first opened. |
+| start-geopoint | Captures GPS coordinates when the form is first opened. Can be used to warm up the device GPS so that later GPS questions can reach accurate readings more quickly. |
 | background-geopoint | Captures GPS coordinates when a specific question is answered. The question must be specified in the <code>trigger</code> column of the <code>background-geopoint</code> question. |
+| background-audio | Records audio in the background while a form is open. To learn more about this feature, see <a href="https://support.kobotoolbox.org/recording-interviews.html">Recording interviews with background audio recording</a>. | 
 | audit | Captures a detailed log of the interview process, including start time, end time, location, and user actions during the entire data collection process. This metadata question is not supported in Enketo.<br><br>To learn more about using the audit question for audit logs and configuring settings, see <a href="https://docs.getodk.org/form-audit-log/">Form Audit Log (ODK)</a>. |
 
 ## Configuring metadata in KoboCollect