docs: tighten concepts

README.md

@@ -56,27 +56,24 @@ document.body.appendChild(tree)
 ```
 
 ## Concepts
-- __state:__ a single object that contains all application state, should only
+- __state:__ a single object that contains __all__ application state
-  ever be modified by `reducers`
 - __reducers:__ synchronous functions that modify `state`
-- __effects:__ asynchronous functions that perform IO. Effects can call
+- __effects:__ asynchronous functions that emit an `action` when done
-  `send()` when done to handle results
+- __subscriptions:__ read-only data sources that emit `action`s for new data
-- __subscriptions:__ streams of data that can either be written to or read from
 ```txt
- ┌───────────────────────────────┐
+  ┌───────────────────────────┐      ┌────────┐
- │                               │      ┌────────┐
   │  ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐  │      │  User  │
   │    ┌─────────────────┐    │      └────────┘
- ├────┼─│  Subscriptions  │ │    │           │
+  ├──┼─│  Subscriptions  │ │  │           │
   │    └─────────────────┘    │           ▼
   │  │ ┌─────────────────┐ │  │      ┌────────┐            ┌────────┐
- └──────│     Effects     │◀─────┼──────┤  DOM   │◀───────────│ Views  │
+  └────│     Effects     │◀───┼──────│  DOM   │◀───────────│ Views  │
      │ └─────────────────┘ │ Actions └────────┘   DOM tree └────────┘
        ┌─────────────────┐    │                                 ▲
-      │ │    Reducers     │◀┼────┘                                 │
+     │ │    Reducers     │◀┼──┘                                 │
        └─────────────────┘                                      │
      │          │          │         ┌────────┐                 │
-                 └─────────────────────▶│ Router │─────────────────┘
+                └───────────────────▶│ Router │─────────────────┘
      └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘  State  └────────┘    State
               Model
 ```