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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 ...
In addition, there is a contiguous range of another 32 noncharacter code points in the BMP: U+FDD0..U+FDEF. Software implementations are free to use these code points for internal use. One particularly useful example of a noncharacter is the code point U+FFFE. This code point has the reverse UTF-16/UCS-2 byte sequence of the byte order mark (U
A range of code points in the S (Special) Zone of the BMP remains unassigned to characters. UCS-2 disallows use of code values for these code points, but UTF-16 allows their use in pairs. Unicode also adopted UTF-16, but in Unicode terminology, the high-half zone elements become "high surrogates" and the low-half zone elements become "low ...
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.
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".
Unicode characters are distinguished by code points, which are conventionally represented by "U+" followed by four, five or six hexadecimal digits, for example U+00AE or U+1D310. Characters in the Basic Multilingual Plane (BMP), containing modern scripts – including many Chinese and Japanese characters – and many symbols, have a 4-digit code.
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]
UTF-16 was devised to break free of the 65,536-character limit of the original Unicode (1.x) without breaking compatibility with the 16-bit encoding. In UTF-16, singletons have the range 0000–D7FF (55,296 code points) and E000–FFFF (8192 code points, 63,488 in total), lead units the range D800–DBFF (1024 code points) and trail units the ...