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@@ -37,3 +37,19 @@ Once the user selects a receiver device to cast to, the popup sends a `shim:/sel
 Cast SDK API calls are translated into Chromecast protocol messages and sent via `node-castv2`. Based on [@GPMDP/electron-chromecast](https://github.com/GPMDP/electron-chromecast), so there are many similarities. The shim and the bridge exchange messages to implement API methods which require communication with the receiver device.
 
 `Session` and `Media` objects have a counterpart object within the bridge. Some messages are routed directly to these objects. For `Session`, these are in the format `bridge:/session/impl_<methodName>`. For `Media`, it's `bridge:/media/impl_<methodName>`.
+
+
+# Messages (WIP)
+
+| Subject | Origin | Destination | Description |
+| --- | --- | --- | --- |
+| `shim:/initialized` | background | shim | Sent after bridge has been created. |
+| `bridge:/discover` | shim | bridge | Starts network discovery. |
+| `shim:/serviceUp` | bridge | shim | Sent when a receiver device has been found. |
+| `shim:/serviceDown` | bridge | shim | Sent when a receiver device has been lost. |
+| `main:/openPopup` | shim | background | Opens the receiver selection popup. |
+| `popup:/assignShim` | background | popup | Provides popup with tab/frame ID for the opener shim so that it can make a direct connection. |
+| `shim:/popupReady` | popup | shim | Sent after popup is ready to be populated. |
+| `popup:/populateReceiverList` | shim | popup | Supplies popup with current `state.receiverList`. |
+| `shim:/selectReceiver` | popup | shim | Sent once a receiver has been selected. |
+