Re: more flexible pipeline for new scripts and characters

From: Doug Ewell <>
Date: Sun, 20 Nov 2011 14:13:18 -0700

I agree completely: there are some situations, or combinations of
situations, where using the PUA and interchanging PUA data will
certainly cause problems, and some where it will not, and in fact can be
quite helpful.

However, the explanation Peter laid out is often not stated publicly,
but boiled down to simplistic edicts like "Avoid the PUA." Many
examples can be found, on this list and elsewhere.

Doug Ewell | Thornton, Colorado, USA | RFC 5645, 4645, UTN #14 | | @DougEwell ­
-----Original Message----- 
From: Peter Constable
Sent: Sunday, November 20, 2011 12:28
Subject: RE: more flexible pipeline for new scripts and characters
From: [] 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.
Received on Sun Nov 20 2011 - 15:16:55 CST

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