Explainer change for separate rate-limits for embedded site

EVENT.md

@@ -980,6 +980,11 @@ were reported.
 
 In order to achieve the privacy goals listed above the API has various rate limits, which can be found [here](https://github.com/WICG/attribution-reporting-api/blob/main/params/chromium-params.md) for Chromium.
 
+Note: Browsers may choose to allow separate limits, e.g. storage limit,
+rate-limits, and destination limits, for the embedded site/origin for specific
+use cases (for example, [AMP](https://amp.dev) pages rendered by an AMP
+cache/viewer provider).
+
 ### Trigger Data
 
 Trigger data, e.g. advertiser-side data, is extremely important for critical use

index.bs

@@ -1869,8 +1869,14 @@ To <dfn>check if cookie-based debugging is allowed</dfn> given a
 
 <h3 algorithm id="obtaining-context-origin">Obtaining context origin</h3>
 
-To obtain the <dfn export for=node>context origin</dfn> of a [=node=] |node|, return |node|'s [=node navigable=]'s
-[=navigable/top-level traversable=]'s [=navigable/active document=]'s [=origin=].
+To obtain the <dfn export for=node>context origin</dfn> of a [=node=] |node|:
+
+1. Optionally, return the embedded origin if it exists.
+1. Return |node|'s [=node navigable=]'s [=navigable/top-level traversable=]'s
+    [=navigable/active document=]'s [=origin=].
+
+Note: The user agent MAY return the embedded origin to allow separate limits
+for specific use cases.
 
 <h3 id="obtaining-randomized-response">Obtaining a randomized response</h3>
 

verbose_debugging_reports.md

@@ -33,7 +33,7 @@ The `body` will contain the following fields for all source debugging reports:
   This will be a string if there was one such site, or a list of strings if
   there were multiple.
 * `source_event_id`: The source registration's `source_event_id`.
-* `source_site`: The top-level site on which the source registration occurred.
+* `source_site`: The top-level site, or the embedded site for specific use cases, on which the source registration occurred.
 
 Additionally:
 
@@ -149,7 +149,7 @@ Additionally:
 * If the trigger was attributed to a source, then the `body` will also contain
   the following fields:
    * `source_event_id`: The source registration's `source_event_id`.
-   * `source_site`: The top-level site on which the source registration
+   * `source_site`: The top-level site, or the embedded site for specific use cases, on which the source registration
       occurred.
    * `source_debug_key`: The source registration's `debug_key`, but omitted if
      the source registration did not contain a valid `debug_key` or