Use of tag characters in a private encoding - is it valid please?

[Mark E. Shoulson]

I guess one could always define one's own set of "tag characters" in the 
PUA and use them exactly as suggested for the regular tag characters (or 
any other way, for that matter.)  Use of PUA characters between 
consenting adults is nothing Unicode is concerned with, right?  Does 
that make it a "higher-level protocol"?  Don't know, don't entirely 
care.  If users agree to treat data a certain way, that's sort of the 
definition of a protocol, and even plain text is a protocol by that 
reasoning.

~mark

On 5/7/24 14:42, Asmus Freytag via Unicode wrote:
> On 5/7/2024 11:16 AM, Erik Carvalhal Miller via Unicode wrote:
>> “The current conformant use of the undeprecated 96 tag characters is 
>> specified in Unicode Technical Standard #51, ‘Unicode Emoji.’  See 
>> ED-14a. emoji tag sequence (ETS) and Annex C, Valid Emoji Tag 
>> Sequences in that specification.”  No, the Standard itself (book or 
>> collection) does not define what emoji tag sequences are or which 
>> ones are valid; but that same Standard points to UTS #51 as the 
>> definitive specification of ETSs for “conformant use” of tag characters. 
>
> Contrary to your reading, the correct interpretation of that passage 
> is one that considers the tag characters as quasi reserved for use 
> with a specific external protocol. The word "current" allows Unicode 
> to later designate other protocols, if desired.
>
> It very clearly does not contemplate any other uses of tag characters, 
> so no, their use with PUA characters (or any other characters) is not 
> conformant in the same way as assigning a PUA code point a private 
> character.
>
> In order to use the tag characters conformantly, you must claim 
> conformance to both TUS and UTS#51.
>
> A./
>
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