From: [email protected] [mailto:[email protected]] On Behalf 
Of Doug Ewell

> This is one of the things the PUA is for.  Unfortunately, it has become 
> very popular to tell people to stay away from the PUA, that it is evil 
> and unsuitable for any sort of interchange

That's an overstatement. Implementing PUA can be very problematic _in some 
scenarios_. For instance, suppose an OS vendor were to implement PUA characters 
for thousands of ideographs, in effect assuming that a large portion of PUA 
were those ideographs. That would lead to a number of problems, including the 
following:

- users interested in using a PUA character for some other purpose would have 
problems

- data would not interoperate between that OS and other platforms

- if those characters later are later added to Unicode, users, app developers 
and the OS vendor have to deal with problems of data using alternate 
representations

At the opposite extreme, suppose an individual user or app developer needs to 
represent something as a PUA character and there is no broad interchange of 
data using that PUA character, then none of the problems mentioned above arise.

Of course, in between there is a range of scenarios involving varying degrees 
of data interchange. The risks will vary depending on the scenario. Anyone 
considering use of PUA in that case should evaluate the potential risks and 
costs of their options. 



Peter


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