ASVisibiliity

_data/nav_docs.yml

@@ -58,6 +58,7 @@
   - debug-tool-ASRangeController
 - title: Advanced Technologies
   items:
+  - asvisibility
   - asenvironment
   - asrunloopqueue
   

_docs/asenvironment.md

@@ -2,11 +2,11 @@
 title: ASEnvironment
 layout: docs
 permalink: /docs/asenvironment.html
-prevPage: debug-tool-ASRangeController.html
+prevPage: asvisibility.html
 nextPage: asrunloopqueue.html
 ---
 
-`ASEnvironment` is an optimized state propagation system that allows the framework to distrubute a variety of important "evironmental" information up and down the node hierarchy. 
+`ASEnvironment` is a performant and scalable way to enable upward and downward propagation of information throughout the node hierarchy. It stores a variety of critical “environmental” metadata, like the trait collection, interface state, hierarchy state, and more. 
 
 Any object that conforms to the `<ASEnvironment>` protocol can propagate specific states defined in an `ASEnvironmentState` up and/or down the ASEnvironment tree. To define how merges of States should happen, specific merge functions can be provided.
 
@@ -16,4 +16,4 @@ This means that whenever a node needs to query something about its environment,
 
 A key operating principle of ASEnvironment is to update values when new subnodes are added or removed. 
 
-**ASEnvironment is currently used internally in the framework. There is no public API available at this time.**
+ASEnvironment powers many of the most valuable features of AsyncDisplayKit. **There is no public API available at this time.**

_docs/asvisibility.md

@@ -0,0 +1,13 @@
+---
+title: ASVisibility
+layout: docs
+permalink: /docs/asvisibility.html
+prevPage: debug-tool-ASRangeController.html
+nextPage: asenvironment.html
+---
+
+`ASNavigationController` and `ASTabBarController` both implement the `ASVisibility` protocol. These classes can be used even without `ASDisplayNodes`, making them suitable base classes for your inheritance hierarchy. For any child view controllers that are `ASViewControllers`, these classes know the exact number of user taps it would take to make the view controller visible (0 if currently visible).
+
+Knowing a view controller’s visibility depth allows view controllers to automatically take appropriate actions as a user approaches or leaves them. Non-default tabs in an app might preload some of their data; a controller 3 levels deep in a navigation stack might progressively free memory for images, text, and fetched data as it gets deeper. 
+
+Any container view controller can implement a simple protocol to integrate with the system. For example, `ASNavigationController` will return a visibility depth of it's own visibilityDepth + 1 for a view controller that would be revealed by tapping the back button once.

_docs/containers-asviewcontroller.md

@@ -8,7 +8,7 @@ nextPage: containers-astablenode.html
 
 `ASViewController` is a subclass of `UIViewController` that adds several useful features for hosting `ASDisplayNode` hierarchies. 
 
-An ASViewController can be used in place of any UIViewController - including within a UINavigationController, UITabBarController and UISpitViewController or as a modal view controller.
+An ASViewController can be used in place of any UIViewController - including within a `UINavigationController`, `UITabBarController` and `UISpitViewController` or as a modal view controller. 
 
 One of the main benefits to using an ASViewController is to save memory. An ASViewController that goes off screen will automatically reduce the size of the fetch data and display ranges of any of its children. This is key for memory management in large applications. 
 

_docs/debug-tool-ASRangeController.md

@@ -3,7 +3,7 @@ title: Range Visualization
 layout: docs
 permalink: /docs/debug-tool-ASRangeController.html
 prevPage: debug-tool-pixel-scaling.html
-nextPage: asenvironment.html
+nextPage: asvisibility.html
 ---
 
 ##Visualize ASRangeController tuning parameters <a href="https://github.com/facebook/AsyncDisplayKit/pull/1390">(PR #1390)</a>