Updating traffic-control docs

docs/traffic-control.md

@@ -13,9 +13,25 @@ Every time you deploy an Aerobatic app to the cloud a unique version id is
 generated that can be appended to the base app URL to force that specific
 version; bypassing the weighted random version selection process.
 ```
-http://<app_name>.aerobaticapp.com?version=<unique_version_id>`
+http://<app_name>.aerobaticapp.com?_version=<unique_version_id>`
 ```
+When a request comes in with the `_version` parameter, a `_version` cookie is set and the browser is redirected to the same URL with the `_version` parameter stripped off. This allows the app to subsequently modify the search portion of the URL without having to worry about maintaining the `_version` (so manual page refreshes won't nuke the version override). 
 
+However once the redirect happens, there's no obvious way for the end user to know they are looking at a pre-release version of the app. You may want to modify the UI in some way (perhaps render a preview banner) if the current version was selected based on an explicit override. In this case the `__config__` [global variable](/docs/index-page#-__config__-global-variable) will have a `versionMethod` property with the value `"urlOverride"`.
+
+~~~js
+var __config__ = {
+    // bunch of other properties here
+    versionId: '123', 
+    versionName: 'version 123',
+    versionMethod:'urlOverride' // or 'randomAssignment'
+};
+~~~
+
+### Reset Override Version
+In order to reset the URL override, direct the browser to `/?_version=reset`. This will cause the `_version` cookie to be cleared and a new version selected based on the traffic control rules. In the preview banner mentioned above, you may want to include a button or link for the end user to invoke this reset URL.
+
+## Use Cases
 The ability to access any version via URL, even if no live traffic is being directed
 to it, opens up a number of streamlined workflows: