diff --git a/doc/sandbox.mdwn b/doc/sandbox.mdwn
index 6ea8cc607..b986176ae 100644
--- a/doc/sandbox.mdwn
+++ b/doc/sandbox.mdwn
@@ -171,3 +171,10 @@ testing
 [[!toc  levels=2]]
 
 [[Mamma Mia]]
+----
+
+[[!format  c """
+void main () {
+    printf("hello, world!");
+}
+"""]]