diff --git a/Design:-msg.parts---description-of-usage.md b/Design:-msg.parts---description-of-usage.md
index f704fc3..1bb7bbf 100644
--- a/Design:-msg.parts---description-of-usage.md
+++ b/Design:-msg.parts---description-of-usage.md
@@ -21,6 +21,7 @@ parts | object | no | push down stack of previous parts objects to allow nested
 The msg is currently considered complete if
 
  -  `msg.parts.index` >= `msg.parts.count` 
+  - however if msg.parts.count == 0 or is undefined then no output is sent.
  -  `msg.complete` exists (is set to any value)
  -  after an optional timeout from the first part to arrive