Returns the conformsTo of an attachment envelope, or undefined when it has none (the reference's extract_optional_object_for_predicate).
undefined
extract_optional_object_for_predicate
EnvelopeError with code InvalidAttachment when the envelope is not an assertion; AmbiguousPredicate when there are several; Cbor when it is not text.
InvalidAttachment
AmbiguousPredicate
Cbor
Returns the conformsTo of an attachment envelope, or
undefinedwhen it has none (the reference'sextract_optional_object_for_predicate).