Re: Why 17 planes?

From: Philippe Verdy <>
Date: Wed, 28 Nov 2012 02:40:33 +0100

Surrogates are already complicated.

My arguments (using exactly the same terminology or demonstration made with
2 surrogates and a variablbe number of bits) were not defending the
extension of the 17 planes for the purpose of the current Unicode or
ISO/IEC 10646 character encoding policy.

But to demonstrate that these 17 planes were enough according to the
current encoding policy (which is the main factor for warrantying that they
will remain enough).

And that for all other purposes, solutions were possible to extend the
repertoire to encodie something else completely outside this current
standard policy (so necessarily for private use, if ever the more-than-2
planes were not enough).

And it will still remain enough place in the remaining planes to define
later a few more surrogates of a new type, if really needed for a future,
upward compatible, standard if it ever comes to reality — such as having an
open registry of corporate logos or glyph designs, managed by registrars,
and served by Internet like Internet domain names (up to the online
delivery of these glyphs or logos with "Internet-hosted fonts"), i.e. for
encoding objects that won't be worth the need to warranty a long term
stability within Unicode/ISO/IEC 10646 themselves, as these encoded objects
will depend largely on the lifetime of exclusive IP rights and are already
not in scope of Unicode/ISO/IEC 10646. And when these technolgoies will be
developed, nothing will prevent the Unicode/ISO/IEC 10646 standards to make
a reference (later) to these mechanisms (for the online delivery of
compatible fonts supporting these standards, both open fonts, or fonts with
private designs, presented as a collection of glyphs in this external
repertoire, plus registered selection rules).

2012/11/28 "Martin J. Dürst" <>

> To this, my mother would say: "Why keep it simple when we can make it
> complicated?".
> Regards, Martin.
> On 2012/11/27 21:01, Philippe Verdy wrote:
>> That's a valid computation if the extension was limited to use only
>> 2-surrogate encodings for supplementary planes.
>> If we could use 3-surrogate encodings, you'd need
>> 3*2ˆn surrogates
>> to encode
>> 2^(3*n)
>> new codepoints.
>> With n=10 (like today), this requires a total of 3072 surrogates, and you
>> encode 2^30 new codepoints. This is still possible today, even if the BMP
>> is almost full and won't allow a new range of 1024 surrogates: you can
>> still use 2 existing surrogates to encode 2048 "hyper-surrogates" in the
>> special plane 16 (or for private use in the private planes 14 and 15),
>> which will combine with the existing low surrogates in the BMP.
Received on Tue Nov 27 2012 - 19:42:48 CST

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