Absolute URI prefixes of external resources that are loaded while SkipExternalResources is true, for example https://cdn.example.com/assets/ or file:///C:/assets/.
Remarks
External resources are not loaded unless the caller allows them: loading a remote or local resource named by an untrusted document can reach internal network addresses, leak Windows credentials through UNC paths, or copy local files into the output. Content carried inside the document (data: and cid: references, packaged parts) is not external and still loads.