--- a/mercurial/commandserver.py	Sun Jan 18 18:49:59 2015 +0900
+++ b/mercurial/commandserver.py	Sun Jan 18 17:55:28 2015 +0900
@@ -78,6 +78,9 @@
 
     data length (unsigned int),
     encoded message and metadata, as a flat key-value dict.
+
+    Each message should have 'type' attribute. Messages of unknown type
+    should be ignored.
     """
 
     # teach ui that write() can take **opts