Update index.bs

Author: andreubotella

index.bs

@@ -191,7 +191,9 @@ except as specified in [[#global-scope]]. [[!HTML]]
 The Global Scope {#global-scope}
 ================================
 
-The exact type of the global scope (`globalThis`) can vary across runtimes. Most Web Platform APIs are defined in terms that assume Web Browser environments that specifically expose types like {{Window}}, {{WorkerGlobalScope}}, and so forth. To simplify conformance, this Standard does not require such global scope interfaces to be supported, but each global scope in a relevant runtime must map to a global scope interface defined in web specifications. All interfaces, methods, and properties defined by this Standard which are required by web specifications to be exposed in a global scope interface shall be exposed on all of the runtime's corresponding global scopes (e.g., `globalThis.crypto`, `globalThis.ReadableStream`, etc).
+The exact type of the global scope (`globalThis`) can vary across runtimes. Most Web Platform APIs are defined in terms that assume Web Browser environments that specifically expose types like {{Window}}, {{WorkerGlobalScope}}, and so forth. To simplify conformance, this Standard does not require such global scope interfaces to be supported, but each global scope in a relevant runtime may be mapped to a global scope interface defined in web specifications. All interfaces, methods, and properties defined by this Standard which are required by web specifications to be exposed in a global scope interface shall be exposed on all of the runtime's corresponding global scopes (e.g., `globalThis.crypto`, `globalThis.ReadableStream`, etc).
+
+Note: It is expected that a runtime's main global scope maps to {{Window}}, that web worker global scopes map to {{WorkerGlobalScope}}, etc. Global scopes that do not map to any global interface could only implement web APIs defined as `[Exposed=*]`.
 
 With many runtimes, adding a new global-scoped property can introduce breaking changes when the new global conflicts with existing application code. Many Web Platform APIs define global properties using [=read only|the `readonly` attribute=]. [[!WEBIDL]] To avoid introducing breaking changes, runtimes conforming to this Standard may omit the `readonly` attribute for properties being added to the global scope. This allows users of these runtimes to delete or overwrite these properties if they conflict with existing application code.