When resources have to be located outside the EPUB container, EPUB creators are RECOMMENDED to reference them via the secure https URI scheme [rfc7230]
Looks like double brackets weren't used on this one.
(The use of URI looks fine here since it's defined in the rfc.)
Section 3.6 has a broken reference to RFC 7230:
Looks like double brackets weren't used on this one.
(The use of URI looks fine here since it's defined in the rfc.)