This part of the standard defines the representation of ID-tags as a 78-position bar-no-bar code (BNB-78) printed in fluorescent ink in area R1 on the reverse side of items. BNB-78 encoding is one of two encoding specifications supported by this standard3) for the printing of ID-tags in area R1, the other being BNB-62, which is specified in part C of the standard. NOTE 1 Representation in the form of a 4-state code printed on the front of the item is covered in S18d. BNB-78 encoding supersedes the earlier specified BNB-62 encoding and shall be applied in all cases in which ID-tags are placed in area R1 on the reverse side of letter mail items of size up to and including C5, by issuers other than those explicitly authorised to continue use of BNB-62 encoding, namely An Post (Ireland), Canada Post and United States Postal Service. NOTE 2 ID-tags encoded in area R1 are required to be compliant with S18 (see UPU standard S19 and article RL 123 of the Letter Post Manual [1]). This supports only two encodings in area R1, namely BNB-78 as defined herein and BNB62 as defined in S18c. The latter is authorised for continued use only by the three issuers mentioned above. Where IDtags are used, and are applied in area R1 on the reverse side of letter mail items of size up to and including C5, the use of BNB-78 encoding is mandatory for all other issuers. NOTE 3 BNB-78 encoding is not considered suitable for use on flats. S18d defines a 4-state encoding which may be used for this purpose.