diff --git a/files/en-us/web/http/headers/content-security-policy/sandbox/index.md b/files/en-us/web/http/headers/content-security-policy/sandbox/index.md
index ec16e338b4cd937..55ee772bca8eab3 100644
--- a/files/en-us/web/http/headers/content-security-policy/sandbox/index.md
+++ b/files/en-us/web/http/headers/content-security-policy/sandbox/index.md
@@ -72,6 +72,8 @@ where `<value>` can optionally be one of the following values:
 - `allow-top-navigation-to-custom-protocols`
   - : Allows navigations to non-`http` protocols built into browser or [registered by a website](/en-US/docs/Web/API/Navigator/registerProtocolHandler/Web-based_protocol_handlers). This feature is also activated by `allow-popups` or `allow-top-navigation` keyword.
 
+> **Note:** The `allow-top-navigation` and related values only make sense for embedded documents (such as child iframes). For standalone documents, these values have no effect, as the top-level browsing context is the document itself.
+
 ## Examples
 
 ```http