diff --git a/Forum-Client.md b/Forum-Client.md
index ac23bfb..969e8ec 100644
--- a/Forum-Client.md
+++ b/Forum-Client.md
@@ -4,13 +4,15 @@ The forum client is a [BSP client](BSP) that synchronises forum posts among grou
 
 The forum client's identifier is `org.briarproject.briar.forum`.
 
-Each forum has its own group. The [group descriptor](BSP#group-identifiers) is a [BDF list](BDF) with two elements: `name` (string) and `salt` (raw). The salt is 32 random bytes, to prevent collisions between forums with the same name.
+Each forum has its own BSP group. The [group descriptor](BSP#group-identifiers) is a [BDF list](BDF) with two elements: `name` (string) and `salt` (raw). The salt is 32 random bytes, to prevent collisions between forums with the same name.
 
 ### Message types
 
 **POST** - The message body is a BDF list with four elements: `parentId` (unique ID or null), `author` (list), `content` (string), and `signature` (raw).
 
-`parentId` is the optional ID of a post in the same group to which this post replies. `author` is a list with three elements: `formatVersion` (int), `nickname` (string), and `publicKey` (raw). The signature covers a BDF list with five elements: `groupId` (unique ID), `timestamp` (int), `parentId` (unique ID or null), `author` (list), and `content` (string). The group ID and timestamp are taken from the message header.
+`parentId` is the optional ID of a post in the same forum to which this post replies. `author` is a list with three elements: `formatVersion` (int), `nickname` (string), and `publicKey` (raw). This identifies the author of the post.
+
+The signature covers a BDF list with five elements: `groupId` (unique ID), `timestamp` (int), `parentId` (unique ID or null), `author` (list), and `content` (string). The group ID and timestamp are taken from the message header.
 
 ### Validity policy