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[a] The encoding is variable-length as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding now known as UCS-2 (for 2-byte Universal Character Set), [1] [2] once it became clear that more than 2 16 (65,536) code points were needed, [3] including most emoji and important CJK ...
The UCS includes 2048 code points in the Basic Multilingual Plane (BMP) for surrogate code point pairs. Together these surrogates allow any code point in the sixteen other planes to be addressed by using two surrogate code points. This provides a simple built-in method for encoding the 20.1 bit UCS within a 16 bit encoding such as UTF-16.
The reserved code points (the "holes") in the alphabetic ranges up to U+1D551 duplicate characters in the Letterlike Symbols block. In order, these are ℎ / ℬ ℰ ℱ ℋ ℐ ℒ ℳ ℛ / ℯ ℊ ℴ / ℭ ℌ ℑ ℜ ℨ / ℂ ℍ ℕ ℙ ℚ ℝ ℤ.
A code point is represented by a sequence of code units. The mapping is defined by the encoding. Thus, the number of code units required to represent a code point depends on the encoding: UTF-8: code points map to a sequence of one, two, three or four code units. UTF-16: code units are twice as long as 8-bit code units.
For example, Alt+0 247 yields a ÷, corresponding to its code point, but the character produced by Alt+2 47 depends on the OEM code page, such as Code page 437, and may yield a ≈. Also Alt + 0 1 2 8 through Alt + 0 1 5 9 yield the characters assigned in rows 8 and 9 in the CP1252 layout , rather than the C1 control codes that are assigned to ...
All code points in the BMP are accessed as a single code unit in UTF-16 encoding and can be encoded in one, two or three bytes in UTF-8. Code points in planes 1 through 16 (the supplementary planes) are accessed as surrogate pairs in UTF-16 and encoded in four bytes in UTF-8.
Code points are commonly used in character encoding, where a code point is a numerical value that maps to a specific character.In character encoding code points usually represent a single grapheme—usually a letter, digit, punctuation mark, or whitespace—but sometimes represent symbols, control characters, or formatting. [4]
The number of code points in each block must be a multiple of 16. A block may contain code points that are reserved, not-assigned, etc. Each character that is assigned, has a single "block name" value from the 338 names assigned as of Unicode version 16.0. Unassigned code points outside of an existing block have the default value "No_block".