Chalkboard feature added.

skald-protocol.md

@@ -355,8 +355,21 @@ chat history, and is not expected to contain user-visible content.
 ```
 
 Currently defined kinds include `error`, `warning`, `info`, `kicked`,
-`clearchat` (not to be confused with the `clearchat` hall action), and
-`mute`.
+`clearchat` (not to be confused with the `clearchat` hall action),
+`chalkboard`, and `mute`.  A `chalkboard` user message carries the current
+virtual chalkboard state:
+
+```javascript
+{
+    type: 'usermessage',
+    kind: 'chalkboard',
+    privileged: true,
+    value: {
+        text: text,
+        revision: revision
+    }
+}
+```
 
 A user action requests that the server act upon a user.
 
@@ -371,7 +384,7 @@ A user action requests that the server act upon a user.
 }
 ```
 Currently defined kinds include `op`, `unop`, `present`, `unpresent`,
-`kick` and `setdata`.
+`chalkboard`, `unchalkboard`, `kick` and `setdata`.
 
 Finally, a hall action requests that the server act on the current hall.
 
@@ -386,8 +399,21 @@ Finally, a hall action requests that the server act on the current hall.
 ```
 
 Currently defined kinds include `clearchat` (not to be confused with the
-`clearchat` user message), `lock`, `unlock`, `record`, `unrecord`,
-`subhalls` and `setdata`.
+`clearchat` user message), `chalkboard`, `lock`, `unlock`, `record`,
+`unrecord`, `subhalls` and `setdata`.  A `chalkboard` hall action updates
+the session-only virtual chalkboard and requires `op`, `admin`, or
+temporary `chalkboard` permission:
+
+```javascript
+{
+    type: 'hallaction',
+    kind: 'chalkboard',
+    value: {
+        text: text,
+        revision: revision
+    }
+}
+```
 
 
 # Peer-to-peer file transfer protocol