From https://once.com/writebook

app/controllers/sections_controller.rb

@@ -0,0 +1,15 @@
+class SectionsController < LeafablesController
+  private
+    def new_leafable
+      Section.new leafable_params
+    end
+
+    def leafable_params
+      params.fetch(:section, {}).permit(:body, :theme)
+        .with_defaults(body: default_body)
+    end
+
+    def default_body
+      params.fetch(:leaf, {})[:title]
+    end
+end