Web and XML Glossary

UCS standardized in ISO 10646 integrates all previous internationally/nationally agreed character sets into a single code set. UCS is based on 4-octet (32-bit) coding scheme known as the "canonical form" (UCS-4), but a 2-octet (16-bit) form (UCS-2) is used for the BMP, where octets 1 and 2 are assumed to be 00 00. The code set is split into 128 "groups" of "planes" containing 256 "rows" with 256 "cells" for characters. Each character is addressed using multiple octets, the third (in UCS-2 the first) of which identifies the row containing the character and the fourth (in UCS-2 the second) its cell number. The first 127 characters of the BMP used for 16-bit code interchange are those of ASCII. The characters forming the second half of the first row are those used in ISO 8859-1.