diff --git a/Serialization.md b/Serialization.md
index 9e95bac..f4be176 100644
--- a/Serialization.md
+++ b/Serialization.md
@@ -22,6 +22,10 @@ We want a format which is:
 * Represents floating-point values faithfully and readably
   * A decimal format would be best
 
+## Behavior
+
+We want write-read and write-read-write round trips to be faithful.
+
 # Framework and format
 
 ## Rust frameworks