Document on_behalf_of field in SubmitInput

Change-Id: I59f596b2bd240d59954ab4d29c7cd833f7d2d514

Documentation/access-control.txt

diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index 0758c5c..76b3569 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -786,7 +786,9 @@
 === Submit (On Behalf Of)
 
 This category permits users who have also been granted the `Submit`
-permission to submit changes on behalf of another user.
+permission to submit changes on behalf of another user, by using the
+`on_behalf_of` field in link:rest-api-changes.html#submit-input[SubmitInput]
+when link:rest-api-changes.html#submit-change[submitting using the REST API].
 
 Note that this permission is named `submitAs` in the `project.config`
 file.

Documentation/rest-api-changes.txt

diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 7a907ba..446c3c6 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -4802,6 +4802,12 @@
 [options="header",cols="1,^1,5"]
 |===========================
 |Field Name      ||Description
+|`on_behalf_of`|optional|
+If set, submit the change on behalf of the given user. The value may take any
+format link:rest-api-accounts.html#account-id[accepted by the accounts REST
+API]. Using this option requires
+link:access-control.html#category_submit_on_behalf_of[Submit (On Behalf Of)]
+permission on the branch.
 |`wait_for_merge`|Deprecated, always `true`|
 Whether the request should wait for the merge to complete.
 |===========================