Re: Private Use Area

From: Asmus Freytag <>
Date: Mon, 18 Feb 2013 10:47:56 -0800

On 2/18/2013 5:43 AM, Erkki I Kolehmainen wrote:
> This looks quite clear to me. If I create something and somebody else uses my creation in the intended context, he agrees to my definition. his agreement is private, outside the standard, since the same code points may represent a multitude of different meanings. It may also be the result of a negotiating process within a special purpose user group.


when you write a standard, you can't avoid the use of technical terms.
One of those is the meaning of "private" used here, as Erkki has so ably

You had written:

> ... about ... "private agreement". That is, I feel a somewhat unfortunate way of explaining the situation. You do not need the agreement of anybody to define your assignments in the Private Use Area. Certainly, if someone then wants to use the font and access an alternate glyph then he or she needs to go along with what you have assigned in order to use the font. To me, that sounds like following the documentation of the font rather than being an agreement.

In order to "interpret" the characters - Unicode's term for any
operation other than "blind" transactions, like copying a string,
requires you to follow some definition of which code point goes with
which encoded character.

You correctly note that a font, in a way, provides a private
specification (private as seen from the point of view of the original
standard, which remains ignorant of it).

No user can correctly use your font without that "specification",
whether you make it available as a document or whether the user "reverse
engineers" it by looking at the font in an editor and recognizing the

By "agreeing" to follow your specification (and not someone else's) your
user now has a "private agreement" with you. Simple as that.

Matters may seem more complex because most software supports, to a
degree, a "generic" treatment of private use characters for the purpose
of rendering only. That is, if the rendering requirements consist of
left-to-right layout of boxes, with their width defined in the font.
then any font using your private assignment of shapes can be rendered
without the software needing to be modified.

That default treatment is, of course, very useful, but it is not
required by the Unicode Standard. In fact, it's an (usually implicit)
private specification by the maker of the software, and by designing a
font that takes advantage of it, you are now in a "private agreement"
with the software maker.

Note that the default treatment for sorting, captilization, and a host
of other functions is not going to work for you or most users, for that
matter, because, unlike the case of fonts, there's no widely supported
data format for submitting details of you to "interpret" a character
outside rendering.

Received on Mon Feb 18 2013 - 12:50:20 CST

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