diff --git a/doc/data/fill-down.csv b/doc/data/fill-down.csv
new file mode 100644
index 000000000..88477a59d
--- /dev/null
+++ b/doc/data/fill-down.csv
@@ -0,0 +1,4 @@
+a,b,c
+1,,3
+4,5,6
+7,,9