How can one know that `the value does not map to a well-known specification`? Some IETF specs (e.g. Web Linking and link relations) mandate that *any* non-standard value must be an URI (e.g. https://www.rfc-editor.org/rfc/rfc8288.html#section-2.1.2). I suggest a similar approach here.
_Originally posted by @pmhsfelix in https://github.com/openid/OpenID4VCI/pull/389#discussion_r1842458096_