Corrigendum #9

Shawn Steele Shawn.Steele at
Mon Jun 2 11:21:23 CDT 2014

That’s what I think is exactly what should be clarified.  A cooperating system of apps should likely use some other markup, however if they want to use FFFF to say “OK to insert ad here” (or whatever), that’s up to them.

I fear that the current wording says “Because you might have a cooperating system of apps that all agree FFFF is ‘OK to insert ad here’, you may as well emit FFFF all the time just in case some other app happens to use the same sentinel”.

The “problem” is now that previously these characters were illegal, so my application didn’t have to explicitly remove them when importing external stuff because they weren’t allowed to be there.  With the wording of the corrigendum, the onus is on every app importing data to filter out these code points because they are “suddenly” legal in foreign data streams.

That is a breaking change for applications, and, worse, it isn’t in the control of the applications that take advantage of the newly laxer wording, but rather all the other applications on the planet, which may have been stable for years.

My interpretation of “interchanged” was “interchanged outside of a system that understood your private use of the noncharacters”.  I can see where that may not have been everyone’s interpretation, and maybe should be updated.  My interpretation of what you’re saying below is “sentinel values with a private meaning can be exchanged between apps”, which is what the PUA’s for.

I don’t mind at all if the definition is loosened somewhat, but if we’re turning them into PUA characters we should just turn them into PUA characters.


From: mark.edward.davis at [mailto:mark.edward.davis at] On Behalf Of Mark Davis ??
Sent: Monday, June 2, 2014 9:08 AM
To: Shawn Steele
Cc: Markus Scherer; Doug Ewell; Unicode Mailing List
Subject: Re: Corrigendum #9

The problem is where to draw the line. In today's world, what's an app? You may have a cooperating system of "apps", where it is perfectly reasonable to interchange sentinel values (for example).

I agree with Markus; I think the FAQ is pretty clear. (And if not, that's where we should make it clearer.)


— Il meglio è l’inimico del bene —

On Mon, Jun 2, 2014 at 6:02 PM, Shawn Steele <Shawn.Steele at<mailto:Shawn.Steele at>> wrote:
I also think that the verbiage swung too far the other way.  Sure, I might need to save or transmit a file to talk to myself later, but apps should be strongly discouraged for using these for interchange with other apps.

Interchange bugs are why nearly any news web site ends up with at least a few articles with mangled apostrophes or whatever (because of encoding differences).  Should authors’ tools or feeds or databases or whatever start emitting non-characters from internal use, then we’re going to have ugly leak into text “everywhere”.

So I’d prefer to see text that better permitted interchange with other components of an application’s internal system or partner system, yet discouraged use for interchange with “foreign” apps.


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