Merge pull request #1046 from akeneo/DXIM-18

DXIM-18 - add doc about context change

Author: JulienVerbrugge

content/extensions/ui-extensions.md

@@ -247,8 +247,6 @@ For `pim.category.tab` position, this parameter is sent:
 
 #### Get PIM data from the iframe
 
-**PostMessage**
-
 To be able to communicate the products or product models selection (from position `pim.product-grid.action-bar`) to the iframe, we use the [PostMessage](https://developer.mozilla.org/docs/Web/API/Window/postMessage) protocol.
 
 After the iframe is loaded, the PIM send an *event* which is a normalized message [MessageEvent](https://developer.mozilla.org/docs/Web/API/MessageEvent) with a field `data` containing our information. 
@@ -309,6 +307,31 @@ Example :
 ```
 After receiving this *event*, the PIM will send a PostMessage *event*, similar to the one sent after the iframe loading.
 
+#### Product and product model context change
+
+The **PIM context** is propagated within the iframe when it changes using **postmessage**. This only applies to the product and product model positions: **pim.product-model.header**, **pim.sub-product-model.header** and **pim.product.header**.
+
+The message contains :
+- A `context` object containing the selected `locale` and `channel`.
+- A `user` object containing the `username` and `groups` of the connected user.
+
+Example :
+```json
+{
+  "context": {
+    "locale": "en_US",
+    "channel": "ecommerce"
+  },
+  "user": {
+    "username": "admin",
+    "groups": [
+      "IT support",
+      "All"
+    ]
+  }
+}
+```
+
 #### Ensuring security of embedded iframes
 
 To help ensuring the security of iframes we recommand using these two solutions: