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Eh... It does have a transitive normative reference to T.61, but only by way of special restrictions on the use of three characters. T61String is defined in terms of ISO 2022, with the default C0 Character set set to ISO-IR-102 (as you linked). ISO-IR-102 defines the set of graphical characters, but also places a condition on the use of 3 of them by reference to T.61. It also requires that the control character set C0 be set to ISO-IR-106 by default, and ISO-IR-107 for C1. The net effect is that the default character set of T61String is almost the T.61 character set, except that to get the T.61 character set, you need to include the escape sequence to set G1 to ISO-IR-103. ESC 2/9 7/6 A conforming T61String implementation does need to support the escape sequences and resulting encodings from ISO-IR-6, ISO-IR-87, ISO-IR-102, ISO-IR-103, ISO-IR-106, ISO-IR-107, ISO-IR-126, ISO-IR-144, ISO-IR-150, ISO-IR-153, ISO-IR-156, ISO-IR-164, ISO-IR-165, ISO-IR-168. Since the control character sets include shift prefixes etc, properly parsing T61Strings into Unicode is non-trivial. This is actually a pretty good reflection of the complexity in ASN.1. Technically the ASN.1 spec proper only requires that a T61 string support exactly the set of characters specified in the above registrations. It does not mandate any particular format, for them. It is the BER encoding that requires that ISO2022 be used to encode these. A different encoding could specify that all strings are encoded as UTF-8, and the different types are just various subsets of allowed characters. |