diff -r b0e0db1565d1 -r 07b58266bce3 mercurial/help/internals/wireprotocolrpc.txt
--- a/mercurial/help/internals/wireprotocolrpc.txt	Mon Aug 27 13:30:44 2018 -0700
+++ b/mercurial/help/internals/wireprotocolrpc.txt	Wed Sep 05 09:06:40 2018 -0700
@@ -514,3 +514,6 @@
    message
       (array of maps) A message describing the error. The message uses the
       same format as those in the ``Human Output Side-Channel`` frame.
+
+TODO formalize when error frames can be seen and how errors can be
+recognized midway through a command response.