Add explanation on schema

examples/todomvc/src/todomvc/db.cljs

@@ -2,12 +2,16 @@
   (:require
     [schema.core :as s :include-macros true]))
 
-
-(def default-initial-state
-  {:todos   (sorted-map)        ;; todo ids are the keys (for sort)
-   :showing :all                ;; one of :all :done or :active
-   })
-
+;; -- Schema ------------------------------------------------------------------
+;;
+;; A Primatic Schema for the contents of `app-db`. At any time we can validate
+;; the contents of 'app-db' using valid schema.
+;;
+;; Only event handlers can mutate "app-db", so after each handler runs  we'll
+;; want to revalidate.
+;;
+;; In handlers.cljs, notice how we use middleware to achieve that.
+;;
 
 (def schema
   {:todos   (s/both (s/pred map?) (s/pred sorted?))
@@ -20,5 +24,15 @@
   (s/validate schema db))
 
 
+;; -- Default Value  ----------------------------------------------------------
+;;
+(def default-value
+  {:todos   (sorted-map)        ;; todo ids are the keys
+   :showing :all
+   })
+
+
+
+