L2/00-391

Clarification of terms relating to 
surrogates and supplementary characters

From: Mark Davis/Cupertino/IBM [mark.davis@us.ibm.com]
Sent: Friday, November 03, 2000 1:51 PM

The editorial committee recommends the clarification of terms relating to
surrogates and supplementary characters. The following is a proposal for
appropriate changes to the glossary. (The committee discussed this via
email. This document reflects the consensus, but not all members were able
to participate.)


A. The current glossary contains inconsistent and incorrect usage of "code
value" and "scalar value". This should be corrected to use the more
consistent terminology of UTR #17: Character Encoding Model: "code point"
and "code unit".


B. Add the following terms to help facilitate common terminology
(especially as people are moving quickly now to support surrogates).

supplementary code point. A Unicode code point between U+10000 and U+10FFFF.

supplementary character. A Unicode encoded character having a supplementary code point.

basic code point. A Unicode code point between U+0000 and U+FFFF. Also known as a BMP code point.

basic character. A Unicode encoded character having a basic code point.


surrogate code point. A Unicode code point in the range U+D800 through
U+DC00. Reserved for use by UTF-16, where a pair of surrogate code units
"stand in" for a supplementary code point. (See high surrogate and low
surrogate.) Note: there is no such thing as a "surrogate" character. That
would be an encoded character having a surrogate code point, which is
impossible.


plane. A range of 65,536 (hex 10000) contiguous code points, where the
first code point is an integer multiple of 65,636 (hex 10000). The Plane
number is the first code point divided by 65,536, so Plane 0 is
U+0000..U+FFFF, Plane 1 is U+10000..U+1FFFF, and Plane 16 is
U+100000..10FFFF. See Basic Multilingual Plane and Supplementary Planes.

Basic Multilingual Plane. Plane 0, consisting of the basic code points.

Supplementary Planes. Planes 1 through 16, consisting of the supplementary
code points.