Is an ASN.1 tag unique if the tag class and the tag number is unique?

Question

An ASN.1 tag consists of two class bits, one form bit and the tag number. My questions is: what is sufficient for tag uniqueness? Is it sufficient, that the class and the number is unique or is it also necessary to include the tag form? Or the other way round: are there two distinct tags which have the same tag class and tag number but a different tag form?

Answer 1

The form (constructed or primitive) is not a part of the tag but is a part of the encoding of a tag under BER. X.680 defines tags in section 8 as class and number. Thus, the distinctiveness of a tag is based on the class and the number.