Unicode - Origin and Development - Architecture and Terminology

Architecture and Terminology

Unicode defines a codespace of 1,114,112 code points in the range 0_hex to 10FFFF_hex. Normally a Unicode code point is referred to by writing "U+" followed by its hexadecimal number. For code points in the Basic Multilingual Plane (BMP), four digits are used (e.g. U+0058 for the character LATIN CAPITAL LETTER X); for code points outside the BMP, five or six digits are used, as required (e.g. U+E0001 for the character LANGUAGE TAG and U+10FFFD for the character PRIVATE USE CHARACTER-10FFFD). Older versions of the standard used similar notations but with slightly different rules. For example, Unicode 3.0 used "U-" followed by eight digits to indicate a code point, and allowed "U+" to be used only with exactly four digits to indicate a code unit, such as a single byte of a multibyte UTF-8 encoding of a code point.