diff --git a/dashjoin-docs/docs/developer-reference.md b/dashjoin-docs/docs/developer-reference.md
index ecc673a6b..b41aceaab 100644
--- a/dashjoin-docs/docs/developer-reference.md
+++ b/dashjoin-docs/docs/developer-reference.md
@@ -49,6 +49,7 @@ Collapsible container with nested widgets
 
 * text: card title
 * roles: show container only if user is in one of these roles
+* expression: optional expression to compute whether the widget's initial expansion state
 
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