diff --git a/NewMutableEncodingDesign.md b/NewMutableEncodingDesign.md
index b3d97dc..c2f712b 100644
--- a/NewMutableEncodingDesign.md
+++ b/NewMutableEncodingDesign.md
@@ -8,6 +8,7 @@ page is about the backend layout that would make those features possible.
  * #795 is about append-only filecaps, #796 is closely related
  * #308 is about deep-traversal dircaps, which will require support from the
    underlying mutable files
+ * [this tahoe-dev message](http://allmydata.org/pipermail/tahoe-dev/2009-July/002345.html) and its neighbors have some good discussion about cap design for mutable files
 
 # Yay ECDSA