Deprecate auto-location

content/ember/v4/auto-location.md

@@ -0,0 +1,42 @@
+---
+id: deprecate-auto-location
+title: AutoLocation Class
+until: '5.0.0'
+since: '4.1.0'
+---
+
+#### Background
+
+Several years ago only some browsers supported the (then) new History Location API.
+Others could only serialize the router location into an url hash `my/path#/ember/route`.
+
+To handle this dynamically, Ember built an AutoLocation that would feature-detect
+and use either 'hash' or 'history' as the underlying mechanism.
+
+These days, virtually all browsers support the history API, so this is what 'auto'
+will resolve to in almost every case. Since 'auto' has served its purpose, it's being removed.
+
+#### Required Changes
+
+Set `locationType` in `config/environment.js` to `'history'`. This is it,
+your app should work just like it used to.
+
+Unless you know for sure that you need to keep feature detection in place (few need that),
+or that you'd like to use the 'hash' location strategy (rarely used in browsers,
+but can be useful for mobile apps delivered via a webview).
+
+#### Advanced Stuff
+
+If you implemented your own Location class and used the `detect` method,
+this one is now deprecated. If you need feature detection you can run your
+detection code in app.js, before setting the location type.
+
+```js
+// app/router.js
+export default class Router extends EmberRouter {
+  location = (historyFeatureDetection() ? 'history' : 'hash');
+  // …
+}
+```
+
+For more background, read the [RFC](https://github.com/emberjs/rfcs/blob/master/text/0711-deprecate-auto-location.md).