Amendment 2 to ITU-T Rec. X.680 | ISO/IEC 8824-1 is expected to be mainly of use to tool builders. It is meant to ensure that they interpret the ASN.1 standard identically as far as mapping values to types is concerned. It specifies:

a)          what is legal ASN.1 and what is not;

b)          the precise value that any value reference name identifies; and

c)          the precise set of values that any type or value set reference name identifies.