Corrigendum #9

[Asmus Freytag]

On 5/31/2014 12:36 PM, Philippe Verdy wrote:
> May be; but there's real doubt that a regular expression that would 
> need this property would be severely broken if that property was 
> corrected. There are many other properties that are more useful (and 
> mich more used) whose associated set of codepoints changes regularly 
> across versions.

we have learned that there are always more implementations of a feature 
than we might have predicted. That has been true, for Unicode, from day one.

More importantly, while a regex that uses an expression that is 
equivalent to "IsInArabiPresentation(x)" may or may not be well-defined, 
there is no reason to break it by splitting the block.

As blocks cannot be discontiguous (unlike other properties), some Arabic 
Presentation forms would have to be put into a new block (Arabic 
Presentation Forms C). This is what would break such expressions - it 
has, in fact, nothing to do with the status of the noncharacters.

There's no reason to contemplate breaking changes of any kind at this point.

A./
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