HTML Guide for allow-storage-access-by-user-activation

The value allow-storage-access-by-user-activation is not a valid keyword for the sandbox attribute of the iframe, as it’s still an experimental value.

The sandbox attribute enables an extra set of restrictions for the content in an iframe. You can add specific keywords to relax certain restrictions, such as allow-scripts, allow-forms, allow-popups, and others.

The experimental value allow-storage-access-by-user-activation is not yet a part of the official list of allowed keywords recognized by the W3C validator or the WHATWG HTML standard.