SR-527 add docs for SR Cross origin iframe recording

pages/docs/session-replay.mdx

@@ -209,3 +209,7 @@ When you enable Session Replay, use the above proxy metric to determine a starti
 #### Am I able to sample our Session Replay collection rate?
 
 Yes, you can configure the percentage of total replays that our SDK will capture as a sampling rate or manually trigger/end replay capture.
+
+#### Can I record cross-origin iframes within my page?
+
+Yes, Session Replay supports recording cross-origin iframes embedded within your page (Web only, SDK v2.77.0+). Both the parent page and child iframe must have the Mixpanel SDK initialized with `record_allowed_iframe_origins` configured to include each other's origins. For detailed setup instructions, see [Cross-Origin Iframe Recording](/docs/tracking-methods/sdks/javascript/javascript-replay#cross-origin-iframe-recording).

pages/docs/tracking-methods/sdks/javascript/javascript-replay.mdx

@@ -264,6 +264,59 @@ List of currently supported remote settings:
 
 Settings that are not yet supported, will not appear in the remote configuration. These non-included options will use the value that was initially set by the user for all `remote_settings_mode` options.
 
+## Cross-Origin Iframe Recording
+
+<Callout type="info">
+Cross-origin iframe recording requires SDK version 2.77.0 or later.
+</Callout>
+
+Session Replay can capture content from cross-origin iframes embedded within your page, providing a unified replay experience across parent pages and embedded third-party content. This is useful when your application embeds widgets, checkout flows, or other cross-origin content that you want to include in your replays.
+
+The SDK handles the communication between parent and child frames automatically using a secure handshake mechanism.
+
+### Configuration
+
+Both the parent page and the child iframe page must be configured to allow cross-origin recording.
+
+#### Parent Page Setup
+
+On your parent page, add the origins of any iframes you want to record to the `record_allowed_iframe_origins` array:
+
+```javascript
+mixpanel.init('YOUR_PROJECT_TOKEN', {
+    record_sessions_percent: 100,
+    record_allowed_iframe_origins: [
+        'https://embedded-widget.example.com',
+        'https://partner-checkout.example.com'
+    ]
+});
+```
+
+#### Child Iframe Page Setup
+
+On the child iframe page, add the parent page's origin to `record_allowed_iframe_origins`:
+
+```javascript
+mixpanel.init('YOUR_PROJECT_TOKEN', {
+    record_sessions_percent: 100,
+    record_allowed_iframe_origins: [
+        'https://yoursite.com'
+    ]
+});
+```
+
+### Origin Format Requirements
+
+Origins must be specified in the format `protocol://domain[:port]`. The SDK performs exact matching, so ensure your origins are formatted correctly.
+
+| Format | Example | Valid |
+|--------|---------|-------|
+| HTTPS domain | `https://example.com` | ✓ |
+| HTTP with port | `http://localhost:3000` | ✓ |
+| No protocol | `example.com` | ✗ |
+| With path | `https://example.com/page` | ✗ |
+| Wildcard | `https://*.example.com` | ✗ |
+
 ## Replay ID
 
 When a replay capture begins, a Replay ID is generated by the SDK and is attached as an event property (`$mp_replay_id`) to events tracked by the SDK during the capture session. Events containing the same `$mp_replay_id` will appear in the same Replay.