   Link: manifest
   Link: license
   Link: canonical
   [ ] Open main menu
     * Home
     * Random
     * Nearby
     * Log in
     * Donate
     * About Wikipedia
     * Disclaimers
   Wikipedia
   _____________________
   Search

                                     UTF-8

   Article Talk
     * Language
     * Watch
     * Edit

   UTF-8 is a variable-width character encoding used for electronic
   communication. Defined by the Unicode Standard, the name is derived from
   Unicode (or Universal Coded Character Set) Transformation Format –
   8-bit.^[1]

                                     UTF-8
   Standard             Unicode Standard                                      
   Classification       Unicode Transformation Format, extended ASCII,        
                        variable-width encoding                               
   Extends              US-ASCII                                              
   Transforms / Encodes ISO 10646 (Unicode)                                   
   Preceded by          UTF-1                                                 
     * v                
     * t                
     * e                

   UTF-8 is capable of encoding all 1,112,064^[nb 1] valid character code
   points in Unicode using one to four one-byte (8-bit) code units. Code
   points with lower numerical values, which tend to occur more frequently,
   are encoded using fewer bytes. It was designed for backward compatibility
   with ASCII: the first 128 characters of Unicode, which correspond
   one-to-one with ASCII, are encoded using a single byte with the same
   binary value as ASCII, so that valid ASCII text is valid UTF-8-encoded
   Unicode as well. Since ASCII bytes do not occur when encoding non-ASCII
   code points into UTF-8, UTF-8 is safe to use within most programming and
   document languages that interpret certain ASCII characters in a special
   way, such as / (slash) in filenames, \ (backslash) in escape sequences,
   and % in printf.

   UTF-8 was designed as a superior alternative to UTF-1, a proposed
   variable-width encoding with partial ASCII compatibility which lacked some
   features including self-synchronization and fully ASCII-compatible
   handling of characters such as slashes. Ken Thompson and Rob Pike produced
   the first implementation for the Plan 9 operating system in September
   1992.^[2]^[3] This led to its adoption by X/Open as its specification for
   FSS-UTF, which would first be officially presented at USENIX in January
   1993 and subsequently adopted by the Internet Engineering Task Force
   (IETF) in RFC 2277 (BCP 18) for future internet standards work, replacing
   Single Byte Character Sets such as Latin-1 in older RFCs.

   UTF-8 is the dominant encoding for the World Wide Web (and internet
   technologies), accounting for 98% of all web pages, and up to 100.0% for
   some languages, as of 2022.^[4]

Contents

     * 1 Naming
     * 2 Encoding
          * 2.1 Examples
          * 2.2 Octal
          * 2.3 Codepage layout
          * 2.4 Overlong encodings
          * 2.5 Invalid sequences and error handling
          * 2.6 Byte order mark
     * 3 Adoption
     * 4 History
          * 4.1 FSS-UTF
     * 5 Standards
     * 6 Comparison with other encodings
          * 6.1 Single-byte
          * 6.2 Other multi-byte
          * 6.3 UTF-16
     * 7 Derivatives
          * 7.1 CESU-8
          * 7.2 MySQL utf8mb3
          * 7.3 Modified UTF-8
          * 7.4 WTF-8
          * 7.5 PEP 383
     * 8 See also
     * 9 Notes
     * 10 References
     * 11 External links

NamingEdit

   The official Internet Assigned Numbers Authority (IANA) code for the
   encoding is "UTF-8".^[5] All letters are upper-case, and the name is
   hyphenated. This spelling is used in all the Unicode Consortium documents
   relating to the encoding.

   However, the name "utf-8" may be used by all standards conforming to the
   IANA list (which include CSS, HTML, XML, and HTTP headers),^[6] as the
   declaration is case-insensitive.^[5]

   Other variants, such as those that omit the hyphen or replace it with a
   space, i.e. "utf8" or "UTF 8", are not accepted as correct by the
   governing standards.^[7] Despite this, most web browsers can understand
   them, and so standards intended to describe existing practice (such as
   HTML5) may effectively require their recognition.^[8]

   Unofficially, UTF-8-BOM and UTF-8-NOBOM are sometimes used for text files
   which contain or don't contain a byte order mark (BOM),
   respectively.^[citation needed] In Japan especially, UTF-8 encoding
   without a BOM is sometimes called "UTF-8N".^[9]^[10]

   Windows XP and later, including all supported Windows versions, have
   codepage 65001, as a synonym for UTF-8 (since Windows 7 support for UTF-8
   is better).^[11] Since Windows 10 version 1903, the default for Windows
   Notepad changed to UTF-8.^[12]^[13]

   In PCL, UTF-8 is called Symbol-ID "18N" (PCL supports 183 character
   encodings, called Symbol Sets, which potentially could be reduced to one,
   18N, that is UTF-8).^[14]

EncodingEdit

   Since the restriction of the Unicode code-space to 21-bit values in 2003,
   UTF-8 is defined to encode code points in one to four bytes, depending on
   the number of significant bits in the numerical value of the code point.
   The following table shows the structure of the encoding. The
   Link: mw-deduplicated-inline-style
   x characters are replaced by the bits of the code point.

                        Code point <-> UTF-8 conversion
First   Last code                                                                                                                      
code    point      Byte 1                       Byte 2                       Byte 3                       Byte 4
point   
                   Link:                        
U+0000  U+007F     mw-deduplicated-inline-style 
                   0xxxxxxx                     
                   Link:                        Link:                        
U+0080  U+07FF     mw-deduplicated-inline-style mw-deduplicated-inline-style 
                   110xxxxx                     10xxxxxx                     
                   Link:                        Link:                        Link:                        
U+0800  U+FFFF     mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                   1110xxxx                     10xxxxxx                     10xxxxxx                     
        ^[nb       Link:                        Link:                        Link:                        Link:                        
U+10000 2]U+10FFFF mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                   11110xxx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     

   The first 128 characters (US-ASCII) need one byte. The next 1,920
   characters need two bytes to encode, which covers the remainder of almost
   all Latin-script alphabets, and also IPA extensions, Greek, Cyrillic,
   Coptic, Armenian, Hebrew, Arabic, Syriac, Thaana and N'Ko alphabets, as
   well as Combining Diacritical Marks. Three bytes are needed for characters
   in the rest of the Basic Multilingual Plane, which contains virtually all
   characters in common use,^[15] including most Chinese, Japanese and Korean
   characters. Four bytes are needed for characters in the other planes of
   Unicode, which include less common CJK characters, various historic
   scripts, mathematical symbols, and emoji (pictographic symbols).

   A "character" can actually take more than 4 bytes; e.g., a national flag
   character takes 8 bytes since it's "constructed from a pair of Unicode
   scalar values".^[16]^[nb 3]

  ExamplesEdit

   Consider the encoding of the euro sign, €:

    1. The Unicode code point for € is U+20AC.
    2. As this code point lies between U+0800 and U+FFFF, this will take
       three bytes to encode.
    3. Hexadecimal
       Link: mw-deduplicated-inline-style
       20AC is binary
       Link: mw-deduplicated-inline-style
       0010 0000 1010 1100. The two leading zeros are added because a
       three-byte encoding needs exactly sixteen bits from the code point.
    4. Because the encoding will be three bytes long, its leading byte starts
       with three 1s, then a 0 (
       Link: mw-deduplicated-inline-style
       1110...)
    5. The four most significant bits of the code point are stored in the
       remaining low order four bits of this byte (
       Link: mw-deduplicated-inline-style
       11100010), leaving 12 bits of the code point yet to be encoded (
       Link: mw-deduplicated-inline-style
       ...0000 1010 1100).
    6. All continuation bytes contain exactly six bits from the code point.
       So the next six bits of the code point are stored in the low order six
       bits of the next byte, and
       Link: mw-deduplicated-inline-style
       10 is stored in the high order two bits to mark it as a continuation
       byte (so
       Link: mw-deduplicated-inline-style
       10000010).
    7. Finally the last six bits of the code point are stored in the low
       order six bits of the final byte, and again
       Link: mw-deduplicated-inline-style
       10 is stored in the high order two bits (
       Link: mw-deduplicated-inline-style
       10101100).

   The three bytes
   Link: mw-deduplicated-inline-style
   11100010
   Link: mw-deduplicated-inline-style
   10000010
   Link: mw-deduplicated-inline-style
   10101100 can be more concisely written in hexadecimal, as
   Link: mw-deduplicated-inline-style
   E2 82 AC.

   The following table summarizes this conversion, as well as others with
   different lengths in UTF-8. The colors indicate how bits from the code
   point are distributed among the UTF-8 bytes. Additional bits added by the
   UTF-8 encoding process are shown in black.

                           Examples of UTF-8 encoding
Character                      Binary code point            Binary UTF-8                 Hex UTF-8                    
                         Link:                        Link: Link:                        Link:                        
$ mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                        U+0024                     010 0100 00100100                     24                           
                         Link:                        Link: Link:                        Link:                        
£ mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                        U+00A3                000 1010 0011 11000010 10100011            C2 A3                        
                         Link:                        Link: Link:                        Link:                        
ह mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                        U+0939          0000 1001 0011 1001 11100000 10100100 10111001   E0 A4 B9                     
                         Link:                        Link: Link:                        Link:                        
€ mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                        U+20AC          0010 0000 1010 1100 11100010 10000010 10101100   E2 82 AC                     
                         Link:                        Link: Link:                        Link:                        
한 mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                        U+D55C          1101 0101 0101 1100 11101101 10010101 10011100   ED 95 9C                     
                         Link:                        Link: Link:                        Link:                        
𐍈 mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                       U+10348   0 0001 0000 0011 0100 1000 11110000 10010000 10001101   F0 90 8D 88                  
                                                            10001000                     

  OctalEdit

   UTF-8's use of six bits per byte to represent the actual characters being
   encoded means that octal notation (which uses 3-bit groups) can aid in the
   comparison of UTF-8 sequences with one another and in manual
   conversion.^[17]

                  Octal code point <-> Octal UTF-8 conversion
First   Last                                                                                                                                                      
code    code     Code point                   Byte 1                       Byte 2                       Byte 3                       Byte 4
point   point    
                 Link:                        Link:                        
000     0177     mw-deduplicated-inline-style mw-deduplicated-inline-style 
                 xxx                          xxx                          
                 Link:                        Link:                        Link:                        
0200    03777    mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                 xxyy                         3xx                          2yy                          
                 Link:                        Link:                        Link:                        Link:                        
04000   077777   mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                 xyyzz                        34x                          2yy                          2zz                          
                 Link:                        Link:                        Link:                        Link:                        
0100000 0177777  mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                 1xyyzz                       35x                          2yy                          2zz                          
                 Link:                        Link:                        Link:                        Link:                        Link:                        
0200000 04177777 mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                 xyyzzww                      36x                          2yy                          2zz                          2ww                          

   With octal notation, the arbitrary octal digits, marked with x, y, z or w
   in the table, will remain unchanged when converting to or from UTF-8.

           Example: Á = U+00C1 =
           Link: mw-deduplicated-inline-style
           0301 (in octal) is encoded as
           Link: mw-deduplicated-inline-style
           303 201 in UTF-8 (C3 81 in hex).
           Example: € = U+20AC =
           Link: mw-deduplicated-inline-style
           020254 is encoded as
           Link: mw-deduplicated-inline-style
           342 202 254 in UTF-8 (E2 82 AC in hex).

  Codepage layoutEdit

   The following table summarizes usage of UTF-8 code units (individual bytes
   or octets) in a code page format. The upper half is for bytes used only in
   single-byte codes, so it looks like a normal code page; the lower half is
   for continuation bytes and leading bytes and is explained further in the
   legend below.

   +---------------------------------------------------------------+
   |UTF-8                                                          |
   |---------------------------------------------------------------|
   |  |0   |1  |2  |3  |4  |5  |6  |7  |8  |9 |A  |B  |C |D |E |F  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |0x|NUL |SOH|STX|ETX|EOT|ENQ|ACK|BEL|BS |HT|LF |VT |FF|CR|SO|SI |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |1x|DLE |DC1|DC2|DC3|DC4|NAK|SYN|ETB|CAN|EM|SUB|ESC|FS|GS|RS|US |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |2x| SP |!  |"  |#  |$  |%  |&  |'  |(  |) |*  |+  |, |- |. |/  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |3x|0   |1  |2  |3  |4  |5  |6  |7  |8  |9 |:  |;  |< |= |> |?  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |4x|@   |A  |B  |C  |D  |E  |F  |G  |H  |I |J  |K  |L |M |N |O  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |5x|P   |Q  |R  |S  |T  |U  |V  |W  |X  |Y |Z  |[  |\ |] |^ |_  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |6x|`   |a  |b  |c  |d  |e  |f  |g  |h  |i |j  |k  |l |m |n |o  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |7x|p   |q  |r  |s  |t  |u  |v  |w  |x  |y |z  |{  || |} |~ |DEL|
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |8x|•   |•  |•  |•  |•  |•  |•  |•  |•  |• |•  |•  |• |• |• |•  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |9x|•   |•  |•  |•  |•  |•  |•  |•  |•  |• |•  |•  |• |• |• |•  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Ax|•   |•  |•  |•  |•  |•  |•  |•  |•  |• |•  |•  |• |• |• |•  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Bx|•   |•  |•  |•  |•  |•  |•  |•  |•  |• |•  |•  |• |• |• |•  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Cx|2   |2  |2  |2  |2  |2  |2  |2  |2  |2 |2  |2  |2 |2 |2 |2  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Dx|2   |2  |2  |2  |2  |2  |2  |2  |2  |2 |2  |2  |2 |2 |2 |2  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Ex|3   |3  |3  |3  |3  |3  |3  |3  |3  |3 |3  |3  |3 |3 |3 |3  |
   |--+----+---+---+---+---+---+---+---+---+--+---+---+--+--+--+---|
   |Fx|4   |4  |4  |4  |4  |4  |4  |4  |5  |5 |5  |5  |6 |6 |  |   |
   +---------------------------------------------------------------+

     7-bit (single-byte) code points. They must not be followed by a
   continuation byte.^[18]
   Link: mw-deduplicated-inline-style
     Continuation bytes.^[19] The tooltip shows in hex the value of the 6
   bits they add.^[nb 4]
   Link: mw-deduplicated-inline-style
     Leading bytes for a sequence of multiple bytes, must be followed by
   exactly N−1 continuation bytes.^[20] The tooltip shows the code point
   range and the Unicode blocks encoded by sequences starting with this byte.
   Link: mw-deduplicated-inline-style
     Leading bytes where not all arrangements of continuation bytes are
   valid.
   Link: mw-deduplicated-inline-style
   E0 and
   Link: mw-deduplicated-inline-style
   F0 could start overlong encodings.
   Link: mw-deduplicated-inline-style
   F4 can start code points greater than U+10FFFF.
   Link: mw-deduplicated-inline-style
   ED can start code points in the range U+D800–U+DFFF, which are invalid
   UTF-16 surrogate halves.^[21]
   Link: mw-deduplicated-inline-style
     Do not appear in a valid UTF-8 sequence.
   Link: mw-deduplicated-inline-style
   C0 and
   Link: mw-deduplicated-inline-style
   C1 could be used only for an "overlong" encoding of a 1-byte
   character.^[22]
   Link: mw-deduplicated-inline-style
   F5 to
   Link: mw-deduplicated-inline-style
   FD are leading bytes of 4-byte or longer sequences that can only encode
   code points larger than U+10FFFF.^[23]
   Link: mw-deduplicated-inline-style
   FE and
   Link: mw-deduplicated-inline-style
   FF were never assigned any meaning.^[24]

  Overlong encodingsEdit

   In principle, it would be possible to inflate the number of bytes in an
   encoding by padding the code point with leading 0s. To encode the euro
   sign € from the above example in four bytes instead of three, it could be
   padded with leading 0s until it was 21 bits long –
   Link: mw-deduplicated-inline-style
   000 000010 000010 101100, and encoded as
   Link: mw-deduplicated-inline-style
   11110000
   Link: mw-deduplicated-inline-style
   10000010
   Link: mw-deduplicated-inline-style
   10000010
   Link: mw-deduplicated-inline-style
   10101100 (or
   Link: mw-deduplicated-inline-style
   F0
   Link: mw-deduplicated-inline-style
   82
   Link: mw-deduplicated-inline-style
   82
   Link: mw-deduplicated-inline-style
   AC in hexadecimal). This is called an overlong encoding.

   The standard specifies that the correct encoding of a code point uses only
   the minimum number of bytes required to hold the significant bits of the
   code point. Longer encodings are called overlong and are not valid UTF-8
   representations of the code point. This rule maintains a one-to-one
   correspondence between code points and their valid encodings, so that
   there is a unique valid encoding for each code point. This ensures that
   string comparisons and searches are well-defined.

  Invalid sequences and error handlingEdit

   Not all sequences of bytes are valid UTF-8. A UTF-8 decoder should be
   prepared for:

     * invalid bytes
     * an unexpected continuation byte
     * a non-continuation byte before the end of the character
     * the string ending before the end of the character (which can happen in
       simple string truncation)
     * an overlong encoding
     * a sequence that decodes to an invalid code point

   Many of the first UTF-8 decoders would decode these, ignoring incorrect
   bits and accepting overlong results. Carefully crafted invalid UTF-8 could
   make them either skip or create ASCII characters such as NUL, slash, or
   quotes. Invalid UTF-8 has been used to bypass security validations in
   high-profile products including Microsoft's IIS web server^[25] and
   Apache's Tomcat servlet container.^[26] RFC 3629 states "Implementations
   of the decoding algorithm MUST protect against decoding invalid
   sequences."^[7] The Unicode Standard requires decoders to "...treat any
   ill-formed code unit sequence as an error condition. This guarantees that
   it will neither interpret nor emit an ill-formed code unit sequence."

   Since RFC 3629 (November 2003), the high and low surrogate halves used by
   UTF-16 (U+D800 through U+DFFF) and code points not encodable by UTF-16
   (those after U+10FFFF) are not legal Unicode values, and their UTF-8
   encoding must be treated as an invalid byte sequence. Not decoding
   unpaired surrogate halves makes it impossible to store invalid UTF-16
   (such as Windows filenames or UTF-16 that has been split between the
   surrogates) as UTF-8,^[27] while it is possible with WTF-8.

   Some implementations of decoders throw exceptions on errors.^[28] This has
   the disadvantage that it can turn what would otherwise be harmless errors
   (such as a "no such file" error) into a denial of service. For instance
   early versions of Python 3.0 would exit immediately if the command line or
   environment variables contained invalid UTF-8.^[29] An alternative
   practice is to replace errors with a replacement character. Since Unicode
   6^[30] (October 2010), the standard (chapter 3) has recommended a "best
   practice" where the error ends as soon as a disallowed byte is
   encountered. In these decoders
   Link: mw-deduplicated-inline-style
   E1,A0,C0 is two errors (2 bytes in the first one). This means an error is
   no more than three bytes long and never contains the start of a valid
   character, and there are 21,952 different possible errors.^[31] The
   standard also recommends replacing each error with the replacement
   character "�" (U+FFFD).

  Byte order markEdit

   If the UTF-16 Unicode byte order mark (BOM, U+FEFF) character is at the
   start of a UTF-8 file, the first three bytes will be
   Link: mw-deduplicated-inline-style
   0xEF,
   Link: mw-deduplicated-inline-style
   0xBB,
   Link: mw-deduplicated-inline-style
   0xBF.

   The Unicode Standard neither requires nor recommends the use of the BOM
   for UTF-8, but warns that it may be encountered at the start of a file
   trans-coded from another encoding.^[32] While ASCII text encoded using
   UTF-8 is backward compatible with ASCII, this is not true when Unicode
   Standard recommendations are ignored and a BOM is added. A BOM can confuse
   software that isn't prepared for it but can otherwise accept UTF-8, e.g.
   programming languages that permit non-ASCII bytes in string literals but
   not at the start of the file. Nevertheless, there was and still is
   software that always inserts a BOM when writing UTF-8, and refuses to
   correctly interpret UTF-8 unless the first character is a BOM (or the file
   only contains ASCII).^[citation needed]

   Some file formats and programming languages have their own way of marking
   usage of encodings like UTF-8 in source code. Examples include HTML <meta
   charset="UTF-8"/> and Python 2.7 # coding: utf-8

AdoptionEdit

   See also: Popularity of text encodings
   [IMG] 
   Enlarge
   Declared character set for 10 million most popular websites since 2010
   [IMG] 
   Enlarge
   Use of the main encodings on the web from 2001 to 2012 as recorded by
   Google,^[33] with UTF-8 overtaking all others in 2008 and over 60% of the
   web in 2012 (since then approaching 100%). The ASCII-only figure includes
   all web pages that only contain ASCII characters, regardless of the
   declared header. Other encodings of Unicode such as GB2312 are added to
   "others".

   Many standards only support UTF-8, e.g. open JSON exchange requires it
   (without a byte order mark (BOM)).^[34] UTF-8 is also the recommendation
   from the WHATWG for HTML and DOM specifications,^[35] and the Internet
   Mail Consortium recommends that all e-mail programs be able to display and
   create mail using UTF-8.^[36]^[37] The World Wide Web Consortium
   recommends UTF-8 as the default encoding in XML and HTML (and not just
   using UTF-8, also declaring it in metadata), "even when all characters are
   in the ASCII range .. Using non-UTF-8 encodings can have unexpected
   results".^[38]

   Lots of software has the ability to read/write UTF-8, though this often
   requires the user to change options from the normal settings, and may
   require a BOM (byte order mark) as the first character to read the file.
   Examples include Microsoft Word^[39]^[40]^[41] and Microsoft
   Excel.^[42]^[43] Most databases support UTF-8 (sometimes the only option
   as with some file formats), including Microsoft's since SQL Server 2019,
   resulting in 35% speed increase, and "nearly 50% reduction in storage
   requirements."^[44]

   UTF-8 has been the most common encoding for the World Wide Web since
   2008.^[45] As of April 2022, UTF-8 accounts for on average 97.6% of all
   web pages (and 985 of the top 1,000 highest ranked web pages).^[4] UTF-8
   includes ASCII as a subset; almost no websites declare only ASCII
   used.^[46] Over a third of the languages tracked have 100.0% UTF-8 use.

   For local text files UTF-8 usage is lower, and many legacy single-byte
   (and CJK multi-byte) encodings remain in use. The primary cause is editors
   that do not display or write UTF-8 unless the first character in a file is
   a byte order mark (BOM), making it impossible for other software to use
   UTF-8 without being rewritten to ignore the byte order mark on input and
   add it on output.^[47]^[48] There has been some improvement, Notepad on
   Windows 10 writes UTF-8 without a BOM by default,^[49] and some system
   files on Windows 11 require UTF-8,^[50] and almost all files on macOS and
   Linux are required to be UTF-8 (without a BOM).^[citation needed] Java 18
   defaults to reading and writing files as UTF-8,^[51] and in older versions
   the NIO API only did so. Many other programming languages default to UTF-8
   for I/O; or plan to migrate to UTF-8, such as Python which already made
   changes to help programmers prepare for the change "to UTF-8 [since it
   has] become the de-facto standard text encoding".^[52]

   Internally in software usage is lower, with UTF-16 or UCS-2 in use,
   particularly on Windows, but also by JavaScript, Python,^[53] Qt, and many
   other cross-platform software libraries. Compatibility with the Windows
   API is the primary reasons for this, though the belief that direct
   indexing of BMP improves speed also was a factor. More recent software has
   started to use UTF-8: the default string primitive used in Go,^[54] Julia,
   Rust, Swift 5,^[55] and PyPy^[56] is UTF-8, a future version of Python
   intends to store strings as UTF-8,^[57] and modern versions of Microsoft
   Visual Studio use UTF-8 internally^[58] (however still require a
   command-line switch to read or write UTF-8^[59]). UTF-8 is the "only text
   encoding mandated to be supported by the C++ standard", as of C++20.^[60]
   As of May 2019, Microsoft reversed its course of only supporting UTF-16
   for the Windows API, providing the ability to set UTF-8 as the "code page"
   for the multi-byte API (previously this was impossible), and now Microsoft
   recommends (programmers) use UTF-8.^[61]

HistoryEdit

   Link: mw-deduplicated-inline-style
   See also: Universal Coded Character Set § History

   The International Organization for Standardization (ISO) set out to
   compose a universal multi-byte character set in 1989. The draft ISO 10646
   standard contained a non-required annex called UTF-1 that provided a byte
   stream encoding of its 32-bit code points. This encoding was not
   satisfactory on performance grounds, among other problems, and the biggest
   problem was probably that it did not have a clear separation between ASCII
   and non-ASCII: new UTF-1 tools would be backward compatible with
   ASCII-encoded text, but UTF-1-encoded text could confuse existing code
   expecting ASCII (or extended ASCII), because it could contain continuation
   bytes in the range 0x21–0x7E that meant something else in ASCII, e.g.,
   0x2F for '/', the Unix path directory separator, and this example is
   reflected in the name and introductory text of its replacement. The table
   below was derived from a textual description in the annex.

                                     UTF-1
   Number   First      Last       Byte 1 Byte 2    Byte 3   Byte 4   Byte 5   
   of bytes code point code point 
   1        U+0000     U+009F     00–9F  
   2        U+00A0     U+00FF     A0     A0–FF     
   2        U+0100     U+4015     A1–F5  21–7E,    
                                         A0–FF     
   3        U+4016     U+38E2D    F6–FB  21–7E,    21–7E,   
                                         A0–FF     A0–FF    
   5        U+38E2E    U+7FFFFFFF FC–FF  21–7E,    21–7E,   21–7E,   21–7E,   
                                         A0–FF     A0–FF    A0–FF    A0–FF    

   In July 1992, the X/Open committee XoJIG was looking for a better
   encoding. Dave Prosser of Unix System Laboratories submitted a proposal
   for one that had faster implementation characteristics and introduced the
   improvement that 7-bit ASCII characters would only represent themselves;
   all multi-byte sequences would include only bytes where the high bit was
   set. The name File System Safe UCS Transformation Format (FSS-UTF) and
   most of the text of this proposal were later preserved in the final
   specification.^[62]^[63]^[64]^[65]

  FSS-UTFEdit

                            FSS-UTF proposal (1992)
Number First     Last                                                                                                                                                        
of     code      code point Byte 1                       Byte 2                       Byte 3                       Byte 4                       Byte 5
bytes  point     
                            Link:                        
1      U+0000    U+007F     mw-deduplicated-inline-style 
                            0xxxxxxx                     
                            Link:                        Link:                        
2      U+0080    U+207F     mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            10xxxxxx                     1xxxxxxx                     
                            Link:                        Link:                        Link:                        
3      U+2080    U+8207F    mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            110xxxxx                     1xxxxxxx                     1xxxxxxx                     
                            Link:                        Link:                        Link:                        Link:                        
4      U+82080   U+208207F  mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            1110xxxx                     1xxxxxxx                     1xxxxxxx                     1xxxxxxx                     
                            Link:                        Link:                        Link:                        Link:                        Link:                        
5      U+2082080 U+7FFFFFFF mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            11110xxx                     1xxxxxxx                     1xxxxxxx                     1xxxxxxx                     1xxxxxxx                     

   In August 1992, this proposal was circulated by an IBM X/Open
   representative to interested parties. A modification by Ken Thompson of
   the Plan 9 operating system group at Bell Labs made it self-synchronizing,
   letting a reader start anywhere and immediately detect character
   boundaries, at the cost of being somewhat less bit-efficient than the
   previous proposal. It also abandoned the use of biases and instead added
   the rule that only the shortest possible encoding is allowed; the
   additional loss in compactness is relatively insignificant, but readers
   now have to look out for invalid encodings to avoid reliability and
   especially security issues. Thompson's design was outlined on September 2,
   1992, on a placemat in a New Jersey diner with Rob Pike. In the following
   days, Pike and Thompson implemented it and updated Plan 9 to use it
   throughout, and then communicated their success back to X/Open, which
   accepted it as the specification for FSS-UTF.^[64]

                       FSS-UTF (1992) / UTF-8 (1993)^[2]
Number First     Last                                                                                                                                                                                     
of     code      code point Byte 1                       Byte 2                       Byte 3                       Byte 4                       Byte 5                       Byte 6
bytes  point     
                            Link:                        
1      U+0000    U+007F     mw-deduplicated-inline-style 
                            0xxxxxxx                     
                            Link:                        Link:                        
2      U+0080    U+07FF     mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            110xxxxx                     10xxxxxx                     
                            Link:                        Link:                        Link:                        
3      U+0800    U+FFFF     mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            1110xxxx                     10xxxxxx                     10xxxxxx                     
                            Link:                        Link:                        Link:                        Link:                        
4      U+10000   U+1FFFFF   mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            11110xxx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     
                            Link:                        Link:                        Link:                        Link:                        Link:                        
5      U+200000  U+3FFFFFF  mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            111110xx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     
                            Link:                        Link:                        Link:                        Link:                        Link:                        Link:                        
6      U+4000000 U+7FFFFFFF mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style mw-deduplicated-inline-style 
                            1111110x                     10xxxxxx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     10xxxxxx                     

   UTF-8 was first officially presented at the USENIX conference in San
   Diego, from January 25 to 29, 1993. The Internet Engineering Task Force
   adopted UTF-8 in its Policy on Character Sets and Languages in RFC 2277
   (BCP 18) for future internet standards work, replacing Single Byte
   Character Sets such as Latin-1 in older RFCs.^[66]

   In November 2003, UTF-8 was restricted by RFC 3629 to match the
   constraints of the UTF-16 character encoding: explicitly prohibiting code
   points corresponding to the high and low surrogate characters removed more
   than 3% of the three-byte sequences, and ending at U+10FFFF removed more
   than 48% of the four-byte sequences and all five- and six-byte sequences.

StandardsEdit

   There are several current definitions of UTF-8 in various standards
   documents:

     * Link: mw-deduplicated-inline-style
       RFC 3629 / STD 63 (2003), which establishes UTF-8 as a standard
       internet protocol element
     * Link: mw-deduplicated-inline-style
       RFC 5198 defines UTF-8 NFC for Network Interchange (2008)
     * ISO/IEC 10646:2014 §9.1 (2014)^[67]
     * The Unicode Standard, Version 11.0 (2018)^[68]

   They supersede the definitions given in the following obsolete works:

     * The Unicode Standard, Version 2.0, Appendix A (1996)
     * ISO/IEC 10646-1:1993 Amendment 2 / Annex R (1996)
     * Link: mw-deduplicated-inline-style
       RFC 2044 (1996)
     * Link: mw-deduplicated-inline-style
       RFC 2279 (1998)
     * The Unicode Standard, Version 3.0, §2.3 (2000) plus Corrigendum #1 :
       UTF-8 Shortest Form (2000)
     * Unicode Standard Annex #27: Unicode 3.1 (2001)^[69]
     * The Unicode Standard, Version 5.0 (2006)^[70]
     * The Unicode Standard, Version 6.0 (2010)^[71]

   They are all the same in their general mechanics, with the main
   differences being on issues such as allowed range of code point values and
   safe handling of invalid input.

Comparison with other encodingsEdit

   Link: mw-deduplicated-inline-style
   See also: Comparison of Unicode encodings

   Some of the important features of this encoding are as follows:

     * Backward compatibility: Backward compatibility with ASCII and the
       enormous amount of software designed to process ASCII-encoded text was
       the main driving force behind the design of UTF-8. In UTF-8, single
       bytes with values in the range of 0 to 127 map directly to Unicode
       code points in the ASCII range. Single bytes in this range represent
       characters, as they do in ASCII. Moreover, 7-bit bytes (bytes where
       the most significant bit is 0) never appear in a multi-byte sequence,
       and no valid multi-byte sequence decodes to an ASCII code-point. A
       sequence of 7-bit bytes is both valid ASCII and valid UTF-8, and under
       either interpretation represents the same sequence of characters.
       Therefore, the 7-bit bytes in a UTF-8 stream represent all and only
       the ASCII characters in the stream. Thus, many text processors,
       parsers, protocols, file formats, text display programs, etc., which
       use ASCII characters for formatting and control purposes, will
       continue to work as intended by treating the UTF-8 byte stream as a
       sequence of single-byte characters, without decoding the multi-byte
       sequences. ASCII characters on which the processing turns, such as
       punctuation, whitespace, and control characters will never be encoded
       as multi-byte sequences. It is therefore safe for such processors to
       simply ignore or pass-through the multi-byte sequences, without
       decoding them. For example, ASCII whitespace may be used to tokenize a
       UTF-8 stream into words; ASCII line-feeds may be used to split a UTF-8
       stream into lines; and ASCII NUL characters can be used to split
       UTF-8-encoded data into null-terminated strings. Similarly, many
       format strings used by library functions like "printf" will correctly
       handle UTF-8-encoded input arguments.
     * Fallback and auto-detection: Only a small subset of possible byte
       strings are a valid UTF-8 string: the bytes C0, C1, and F5 through FF
       cannot appear, and bytes with the high bit set must be in pairs, and
       other requirements. It is extremely unlikely that a readable text in
       any extended ASCII is valid UTF-8. Part of the popularity of UTF-8 is
       due to it providing a form of backward compatibility for these as
       well. A UTF-8 processor which erroneously receives extended ASCII as
       input can thus "auto-detect" this with very high reliability. Fallback
       errors will be false negatives, and these will be rare. Moreover, in
       many applications, such as text display, the consequence of incorrect
       fallback is usually slight.^[original research?] A UTF-8 stream may
       simply contain errors, resulting in the auto-detection scheme
       producing false positives; but auto-detection is successful in the
       majority of cases, especially with longer texts, and is widely used.
       It also works to "fall back" or replace 8-bit bytes using the
       appropriate code-point for a legacy encoding only when errors in the
       UTF-8 are detected, allowing recovery even if UTF-8 and legacy
       encoding is concatenated in the same file.
     * Prefix code: The first byte indicates the number of bytes in the
       sequence. Reading from a stream can instantaneously decode each
       individual fully received sequence, without first having to wait for
       either the first byte of a next sequence or an end-of-stream
       indication. The length of multi-byte sequences is easily determined by
       humans as it is simply the number of high-order 1s in the leading
       byte. An incorrect character will not be decoded if a stream ends
       mid-sequence.
     * Self-synchronization: The leading bytes and the continuation bytes do
       not share values (continuation bytes start with the bits
       Link: mw-deduplicated-inline-style
       10 while single bytes start with
       Link: mw-deduplicated-inline-style
       0 and longer lead bytes start with
       Link: mw-deduplicated-inline-style
       11). This means a search will not accidentally find the sequence for
       one character starting in the middle of another character. It also
       means the start of a character can be found from a random position by
       backing up at most 3 bytes to find the leading byte. An incorrect
       character will not be decoded if a stream starts mid-sequence, and a
       shorter sequence will never appear inside a longer one.
     * Sorting order: The chosen values of the leading bytes means that a
       list of UTF-8 strings can be sorted in code point order by sorting the
       corresponding byte sequences.

  Single-byteEdit

     * UTF-8 can encode any Unicode character, avoiding the need to figure
       out and set a "code page" or otherwise indicate what character set is
       in use, and allowing output in multiple scripts at the same time. For
       many scripts there have been more than one single-byte encoding in
       usage, so even knowing the script was insufficient information to
       display it correctly.
     * The bytes 0xFE and 0xFF do not appear, so a valid UTF-8 stream never
       matches the UTF-16 byte order mark and thus cannot be confused with
       it. The absence of 0xFF (0377) also eliminates the need to escape this
       byte in Telnet (and FTP control connection).
     * UTF-8 encoded text is larger than specialized single-byte encodings
       except for plain ASCII characters. In the case of scripts which used
       8-bit character sets with non-Latin characters encoded in the upper
       half (such as most Cyrillic and Greek alphabet code pages), characters
       in UTF-8 will be double the size. For some scripts, such as Thai and
       Devanagari (which is used by various South Asian languages),
       characters will triple in size. There are even examples where a single
       byte turns into a composite character in Unicode and is thus six times
       larger in UTF-8. This has caused objections in India and other
       countries.
     * It is possible in UTF-8 (or any other multi-byte encoding) to split or
       truncate a string in the middle of a character. If the two pieces are
       not re-appended later before interpretation as characters, this can
       introduce an invalid sequence at both the end of the previous section
       and the start of the next, and some decoders will not preserve these
       bytes and result in data loss. Because UTF-8 is self-synchronizing
       this will however never introduce a different valid character, and it
       is also fairly easy to move the truncation point backward to the start
       of a character.
     * If the code points are all the same size, measurements of a fixed
       number of them is easy. Due to ASCII-era documentation where
       "character" is used as a synonym for "byte" this is often considered
       important. However, by measuring string positions using bytes instead
       of "characters" most algorithms can be easily and efficiently adapted
       for UTF-8. Searching for a string within a long string can for example
       be done byte by byte; the self-synchronization property prevents false
       positives.

  Other multi-byteEdit

     * UTF-8 can encode any Unicode character. Files in different scripts can
       be displayed correctly without having to choose the correct code page
       or font. For instance, Chinese and Arabic can be written in the same
       file without specialized markup or manual settings that specify an
       encoding.
     * UTF-8 is self-synchronizing: character boundaries are easily
       identified by scanning for well-defined bit patterns in either
       direction. If bytes are lost due to error or corruption, one can
       always locate the next valid character and resume processing. If there
       is a need to shorten a string to fit a specified field, the previous
       valid character can easily be found. Many multi-byte encodings such as
       Shift JIS are much harder to resynchronize. This also means that
       byte-oriented string-searching algorithms can be used with UTF-8 (as a
       character is the same as a "word" made up of that many bytes),
       optimized versions of byte searches can be much faster due to hardware
       support and lookup tables that have only 256 entries.
       Self-synchronization does however require that bits be reserved for
       these markers in every byte, increasing the size.
     * Efficient to encode using simple bitwise operations. UTF-8 does not
       require slower mathematical operations such as multiplication or
       division (unlike Shift JIS, GB 2312 and other encodings).
     * UTF-8 will take more space than a multi-byte encoding designed for a
       specific script. East Asian legacy encodings generally used two bytes
       per character yet take three bytes per character in UTF-8.

  UTF-16Edit

     * Byte encodings and UTF-8 are represented by byte arrays in programs,
       and often nothing needs to be done to a function when converting
       source code from a byte encoding to UTF-8. UTF-16 is represented by
       16-bit word arrays, and converting to UTF-16 while maintaining
       compatibility with existing ASCII-based programs (such as was done
       with Windows) requires every API and data structure that takes a
       string to be duplicated, one version accepting byte strings and
       another version accepting UTF-16. If backward compatibility is not
       needed, all string handling still must be modified.
     * Text encoded in UTF-8 will be smaller than the same text encoded in
       UTF-16 if there are more code points below U+0080 than in the range
       U+0800..U+FFFF. This is true for all modern European languages. It is
       often true even for languages like Chinese, due to the large number of
       spaces, newlines, digits, and HTML markup in typical files.
     * Most communication (e.g. HTML and IP) and storage (e.g. for Unix) was
       designed for a stream of bytes. A UTF-16 string must use a pair of
       bytes for each code unit:
          * The order of those two bytes becomes an issue and must be
            specified in the UTF-16 protocol, such as with a byte order mark.
          * If an odd number of bytes is missing from UTF-16, the whole rest
            of the string will be meaningless text. Any bytes missing from
            UTF-8 will still allow the text to be recovered accurately
            starting with the next character after the missing bytes.

DerivativesEdit

   The following implementations show slight differences from the UTF-8
   specification. They are incompatible with the UTF-8 specification and may
   be rejected by conforming UTF-8 applications.

  CESU-8Edit

   Link: mw-deduplicated-inline-style
   Main article: CESU-8

   Unicode Technical Report #26^[72] assigns the name CESU-8 to a nonstandard
   variant of UTF-8, in which Unicode characters in supplementary planes are
   encoded using six bytes, rather than the four bytes required by UTF-8.
   CESU-8 encoding treats each half of a four-byte UTF-16 surrogate pair as a
   two-byte UCS-2 character, yielding two three-byte UTF-8 characters, which
   together represent the original supplementary character. Unicode
   characters within the Basic Multilingual Plane appear as they would
   normally in UTF-8. The Report was written to acknowledge and formalize the
   existence of data encoded as CESU-8, despite the Unicode Consortium
   discouraging its use, and notes that a possible intentional reason for
   CESU-8 encoding is preservation of UTF-16 binary collation.

   CESU-8 encoding can result from converting UTF-16 data with supplementary
   characters to UTF-8, using conversion methods that assume UCS-2 data,
   meaning they are unaware of four-byte UTF-16 supplementary characters. It
   is primarily an issue on operating systems which extensively use UTF-16
   internally, such as Microsoft Windows.^[citation needed]

   In Oracle Database, the UTF8 character set uses CESU-8 encoding, and is
   deprecated. The AL32UTF8 character set uses standards-compliant UTF-8
   encoding, and is preferred.^[73]^[74]

   CESU-8 is prohibited for use in HTML5 documents.^[75]^[76]^[77]

  MySQL utf8mb3Edit

   In MySQL, the utf8mb3 character set is defined to be UTF-8 encoded data
   with a maximum of three bytes per character, meaning only Unicode
   characters in the Basic Multilingual Plane (i.e. from UCS-2) are
   supported. Unicode characters in supplementary planes are explicitly not
   supported. utf8mb3 is deprecated in favor of the utf8mb4 character set,
   which uses standards-compliant UTF-8 encoding. utf8 is an alias for
   utf8mb3, but is intended to become an alias to utf8mb4 in a future release
   of MySQL.^[78] It is possible, though unsupported, to store CESU-8 encoded
   data in utf8mb3, by handling UTF-16 data with supplementary characters as
   though it is UCS-2.

  Modified UTF-8Edit

   Modified UTF-8 (MUTF-8) originated in the Java programming language. In
   Modified UTF-8, the null character (U+0000) uses the two-byte overlong
   encoding
   Link: mw-deduplicated-inline-style
   11000000
   Link: mw-deduplicated-inline-style
   10000000 (hexadecimal
   Link: mw-deduplicated-inline-style
   C0
   Link: mw-deduplicated-inline-style
   80), instead of
   Link: mw-deduplicated-inline-style
   00000000 (hexadecimal
   Link: mw-deduplicated-inline-style
   00).^[79] Modified UTF-8 strings never contain any actual null bytes but
   can contain all Unicode code points including U+0000,^[80] which allows
   such strings (with a null byte appended) to be processed by traditional
   null-terminated string functions. All known Modified UTF-8 implementations
   also treat the surrogate pairs as in CESU-8.

   In normal usage, the language supports standard UTF-8 when reading and
   writing strings through InputStreamReader and OutputStreamWriter (if it is
   the platform's default character set or as requested by the program).
   However it uses Modified UTF-8 for object serialization^[81] among other
   applications of DataInput and DataOutput, for the Java Native
   Interface,^[82] and for embedding constant strings in class files.^[83]

   The dex format defined by Dalvik also uses the same modified UTF-8 to
   represent string values.^[84] Tcl also uses the same modified UTF-8^[85]
   as Java for internal representation of Unicode data, but uses strict
   CESU-8 for external data.

  WTF-8Edit

   This section contains a list of miscellaneous information. Please relocate 
   any relevant information into other sections or articles. (August 2020)    

   In WTF-8 (Wobbly Transformation Format, 8-bit) unpaired surrogate halves
   (U+D800 through U+DFFF) are allowed.^[86] This is necessary to store
   possibly-invalid UTF-16, such as Windows filenames. Many systems that deal
   with UTF-8 work this way without considering it a different encoding, as
   it is simpler.^[87]

   (The term "WTF-8" has also been used humorously to refer to erroneously
   doubly-encoded UTF-8^[88]^[89] sometimes with the implication that CP1252
   bytes are the only ones encoded.)^[90]

  PEP 383Edit

   Version 3 of the Python programming language treats each byte of an
   invalid UTF-8 bytestream as an error (see also changes with new UTF-8 mode
   in Python 3.7^[91]); this gives 128 different possible errors. Extensions
   have been created to allow any byte sequence that is assumed to be UTF-8
   to be losslessly transformed to UTF-16 or UTF-32, by translating the 128
   possible error bytes to reserved code points, and transforming those code
   points back to error bytes to output UTF-8. The most common approach is to
   translate the codes to U+DC80...U+DCFF which are low (trailing) surrogate
   values and thus "invalid" UTF-16, as used by Python's PEP 383 (or
   "surrogateescape") approach.^[92] Another encoding called MirBSD OPTU-8/16
   converts them to U+EF80...U+EFFF in a Private Use Area.^[93] In either
   approach, the byte value is encoded in the low eight bits of the output
   code point.

   These encodings are very useful because they avoid the need to deal with
   "invalid" byte strings until much later, if at all, and allow "text" and
   "data" byte arrays to be the same object. If a program wants to use UTF-16
   internally these are required to preserve and use filenames that can use
   invalid UTF-8;^[94] as the Windows filesystem API uses UTF-16, the need to
   support invalid UTF-8 is less there.^[92]

   For the encoding to be reversible, the standard UTF-8 encodings of the
   code points used for erroneous bytes must be considered invalid. This
   makes the encoding incompatible with WTF-8 or CESU-8 (though only for 128
   code points). When re-encoding it is necessary to be careful of sequences
   of error code points which convert back to valid UTF-8, which may be used
   by malicious software to get unexpected characters in the output, though
   this cannot produce ASCII characters so it is considered comparatively
   safe, since malicious sequences (such as cross-site scripting) usually
   rely on ASCII characters.^[94]

See alsoEdit

     * Alt code
     * Comparison of email clients § Features
     * Comparison of Unicode encodings
          * GB 18030
          * UTF-EBCDIC
     * Iconv
     * Percent-encoding § Current standard
     * Specials (Unicode block)
     * Unicode and email
     * Unicode and HTML
          * Character encodings in HTML

NotesEdit

    1. ^ 17 planes times 2^16 code points per plane, minus 2^11
       technically-invalid surrogates.
    2. ^ The earlier RFC2279 allowed UTF-8 encoding through code point
       U+7FFFFFF. But the current RFC3629 §3 limits UTF-8 encoding through
       code point U+10FFFF, to match the limits of UTF-16.
    3. ^ Some complex emoji characters can take even more than this; the
       transgender flag emoji (🏳️‍⚧️), which consists of the five-codepoint
       sequence U+1F3F3 U+FE0F U+200D U+26A7 U+FE0F, requires sixteen bytes
       to encode, while that for the flag of Scotland (🏴󠁧󠁢󠁳󠁣󠁴󠁿) requires a
       total of twenty-eight bytes for the seven-codepoint sequence U+1F3F4
       U+E0067 U+E0062 U+E0073 U+E0063 U+E0074 U+E007F.
    4. ^ For example, cell
       Link: mw-deduplicated-inline-style
       9D says +1D. The hexadecimal number 9D in binary is
       Link: mw-deduplicated-inline-style
       10011101, and since the 2 highest bits (
       Link: mw-deduplicated-inline-style
       10) are reserved for marking this as a continuation byte, the
       remaining 6 bits (
       Link: mw-deduplicated-inline-style
       011101) have a hexadecimal value of 1D.

ReferencesEdit

   Link: mw-deduplicated-inline-style
    1. ^
       Link: mw-deduplicated-inline-style
       "Chapter 2. General Structure". The Unicode Standard (6.0 ed.).
       Mountain View, California, US: The Unicode Consortium.
       ISBN 978-1-936213-01-6.
    2. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       Pike, Rob (30 April 2003). "UTF-8 history".
    3. ^
       Link: mw-deduplicated-inline-style
       Pike, Rob; Thompson, Ken (1993). "Hello World or Καλημέρα κόσμε or
       こんにちは 世界" (PDF). Proceedings of the Winter 1993 USENIX Conference.
    4. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       "Usage Survey of Character Encodings broken down by Ranking".
       w3techs.com. Retrieved 2022-04-02.
    5. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       "Character Sets". Internet Assigned Numbers Authority. 2013-01-23.
       Retrieved 2013-02-08.
    6. ^
       Link: mw-deduplicated-inline-style
       Dürst, Martin. "Setting the HTTP charset parameter". W3C. Retrieved
       2013-02-08.
    7. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       Yergeau, F. (2003). UTF-8, a transformation format of ISO 10646.
       Internet Engineering Task Force. doi:10.17487/RFC3629. RFC 3629.
       Retrieved 2015-02-03.
    8. ^
       Link: mw-deduplicated-inline-style
       "Encoding Standard § 4.2. Names and labels". WHATWG. Retrieved
       2018-04-29.
    9. ^
       Link: mw-deduplicated-inline-style
       "BOM". suikawiki (in Japanese). Retrieved 2013-04-26.
   10. ^
       Link: mw-deduplicated-inline-style
       Davis, Mark. "Forms of Unicode". IBM. Archived from the original on
       2005-05-06. Retrieved 2013-09-18.
   11. ^
       Link: mw-deduplicated-inline-style
       Liviu (2014-02-07). "UTF-8 codepage 65001 in Windows 7 - part I".
       Retrieved 2018-01-30. Previously under XP (and, unverified, but
       probably Vista, too) for loops simply did not work while codepage
       65001 was active
   12. ^
       Link: mw-deduplicated-inline-style
       Srinivasan, Ramesh (23 May 2021). "How to Change the Default Character
       Encoding in Notepad". Winhelponline Blog. Retrieved 2021-10-20.
   13. ^
       Link: mw-deduplicated-inline-style
       Doan, Kim (2 December 2020). "How to Set Default UTF-8 encoding for
       New Notepad Documents When Saving File". KimConnect.com. Retrieved
       2021-10-20.
   14. ^
       Link: mw-deduplicated-inline-style
       "HP PCL Symbol Sets | Printer Control Language (PCL & PXL) Support
       Blog". 2015-02-19. Archived from the original on 2015-02-19. Retrieved
       2018-01-30.
   15. ^
       Link: mw-deduplicated-inline-style
       Allen, Julie D.; Anderson, Deborah; Becker, Joe; Cook, Richard, eds.
       (2012). "The Unicode Standard, Version 6.1". Mountain View,
       California: Unicode Consortium. {{cite journal}}: Cite journal
       requires |journal= (help)
   16. ^
       Link: mw-deduplicated-inline-style
       "Apple Developer Documentation". developer.apple.com. Retrieved
       2021-03-15.
   17. ^
       Link: mw-deduplicated-inline-style
       "BinaryString (flink 1.9-SNAPSHOT API)". ci.apache.org. Retrieved
       2021-03-24.
   18. ^
       Link: mw-deduplicated-inline-style
       "Chapter 3" (PDF), The Unicode Standard, p. 54
   19. ^
       Link: mw-deduplicated-inline-style
       "Chapter 3" (PDF), The Unicode Standard, p. 55
   20. ^
       Link: mw-deduplicated-inline-style
       "Chapter 3" (PDF), The Unicode Standard, p. 55
   21. ^
       Link: mw-deduplicated-inline-style
       Yergeau, F. (November 2003). UTF-8, a transformation format of ISO
       10646. IETF. doi:10.17487/RFC3629. STD 63. RFC 3629. Retrieved August
       20, 2020.
   22. ^
       Link: mw-deduplicated-inline-style
       "Chapter 3" (PDF), The Unicode Standard, p. 54
   23. ^
       Link: mw-deduplicated-inline-style
       Yergeau, F. (November 2003). UTF-8, a transformation format of ISO
       10646. IETF. doi:10.17487/RFC3629. STD 63. RFC 3629. Retrieved August
       20, 2020.
   24. ^
       Link: mw-deduplicated-inline-style
       "Chapter 3" (PDF), The Unicode Standard, p. 55
   25. ^
       Link: mw-deduplicated-inline-style
       Marin, Marvin (2000-10-17). "Web Server Folder Traversal MS00-078".
   26. ^
       Link: mw-deduplicated-inline-style
       "Summary for CVE-2008-2938". National Vulnerability Database.
   27. ^
       Link: mw-deduplicated-inline-style
       "PEP 529 -- Change Windows filesystem encoding to UTF-8". Python.org.
       Retrieved 2021-08-27. This PEP proposes changing the default
       filesystem encoding on Windows to utf-8, and changing all filesystem
       functions to use the Unicode APIs for filesystem paths. [..] can
       correctly round-trip all characters used in paths (on POSIX with
       surrogateescape handling; on Windows because str maps to the native
       representation). On Windows bytes cannot round-trip all characters
       used in paths
   28. ^
       Link: mw-deduplicated-inline-style
       "DataInput (Java Platform SE 8)". docs.oracle.com. Retrieved
       2021-03-24.
   29. ^
       Link: mw-deduplicated-inline-style
       "Non-decodable Bytes in System Character Interfaces". python.org.
       2009-04-22. Retrieved 2014-08-13.
   30. ^
       Link: mw-deduplicated-inline-style
       "Unicode 6.0.0".
   31. ^ 128 1-byte, (16+5)×64 2-byte, and 5×64×64 3-byte. There may be
       somewhat fewer if more precise tests are done for each continuation
       byte.
   32. ^
       Link: mw-deduplicated-inline-style
       "Chapter 2" (PDF), The Unicode Standard, p. 30
   33. ^
       Link: mw-deduplicated-inline-style
       Davis, Mark (2012-02-03). "Unicode over 60 percent of the web".
       Official Google Blog. Archived from the original on 2018-08-09.
       Retrieved 2020-07-24.
   34. ^
       Link: mw-deduplicated-inline-style
       Bray, Tim (December 2017). "The JavaScript Object Notation (JSON) Data
       Interchange Format". IETF. Retrieved 16 February 2018. {{cite
       journal}}: Cite journal requires |journal= (help)
   35. ^
       Link: mw-deduplicated-inline-style
       "Encoding Standard". encoding.spec.whatwg.org. Retrieved 2020-04-15.
   36. ^
       Link: mw-deduplicated-inline-style
       "Usage of Internet Mail in The World Characters".
       washingtonindependent.com. 1998-08-01. Retrieved 2007-11-08.
   37. ^
       Link: mw-deduplicated-inline-style
       "Encoding Standard". encoding.spec.whatwg.org. Retrieved 2018-11-15.
   38. ^
       Link: mw-deduplicated-inline-style
       "Specifying the document's character encoding". HTML5.2. World Wide
       Web Consortium. 14 December 2017. Retrieved 2018-06-03.
   39. ^
       Link: mw-deduplicated-inline-style
       "Choose text encoding when you open and save files".
       support.microsoft.com. Retrieved 2021-11-01.
   40. ^
       Link: mw-deduplicated-inline-style
       "utf 8 - Character encoding of Microsoft Word DOC and DOCX files?".
       Stack Overflow. Retrieved 2021-11-01.
   41. ^
       Link: mw-deduplicated-inline-style
       "Exporting a UTF-8 .txt file from Word".{{cite web}}: CS1 maint:
       url-status (link)
   42. ^
       Link: mw-deduplicated-inline-style
       "excel - Are XLSX files UTF-8 encoded by definition?". Stack Overflow.
       Retrieved 2021-11-01.
   43. ^
       Link: mw-deduplicated-inline-style
       "How to open UTF-8 CSV file in Excel without mis-conversion of
       characters in Japanese and Chinese language for both Mac and
       Windows?". answers.microsoft.com. Retrieved 2021-11-01.
   44. ^
       Link: mw-deduplicated-inline-style
       "Introducing UTF-8 support for SQL Server".
       techcommunity.microsoft.com. 2019-07-02. Retrieved 2021-08-24. For
       example, changing an existing column data type from NCHAR(10) to
       CHAR(10) using an UTF-8 enabled collation, translates into nearly 50%
       reduction in storage requirements. [..] In the ASCII range, when doing
       intensive read/write I/O on UTF-8, we measured an average 35%
       performance improvement over UTF-16 using clustered tables with a
       non-clustered index on the string column, and an average 11%
       performance improvement over UTF-16 using a heap.
   45. ^
       Link: mw-deduplicated-inline-style
       Davis, Mark (2008-05-05). "Moving to Unicode 5.1". Retrieved
       2021-02-19.
   46. ^
       Link: mw-deduplicated-inline-style
       "Usage Statistics and Market Share of US-ASCII for Websites, October
       2021". w3techs.com. Retrieved 2020-11-01.
   47. ^
       Link: mw-deduplicated-inline-style
       "How can I make Notepad to save text in UTF-8 without the BOM?". Stack
       Overflow. Retrieved 2021-03-24.
   48. ^
       Link: mw-deduplicated-inline-style
       Galloway, Matt. "Character encoding for iOS developers. Or UTF-8 what
       now?". www.galloway.me.uk. Retrieved 2021-01-02. in reality, you
       usually just assume UTF-8 since that is by far the most common
       encoding.
   49. ^
       Link: mw-deduplicated-inline-style
       "Windows 10 Notepad is Getting Better UTF-8 Encoding Support".
       BleepingComputer. Retrieved 2021-03-24. Microsoft is now defaulting to
       saving new text files as UTF-8 without BOM as shown below.
   50. ^
       Link: mw-deduplicated-inline-style
       "Customize the Windows 11 Start menu". docs.microsoft.com. Retrieved
       2021-06-29. Make sure your LayoutModification.json uses UTF-8
       encoding.
   51. ^
       Link: mw-deduplicated-inline-style
       "JEP 400: UTF-8 by Default". openjdk.java.net. Retrieved 2022-03-30.
   52. ^
       Link: mw-deduplicated-inline-style
       "PEP 597 -- Add optional EncodingWarning". Python.org. Retrieved
       2021-08-24.
   53. ^ Python 2 and early 3 versions on Windows, on Unix it used UTF-32.
       Newer Python 3 implementations use all three of ISO-8859-1, UCS-2, and
       UTF-32, depending on the maximum code point needed.
   54. ^
       Link: mw-deduplicated-inline-style
       "The Go Programming Language Specification". Retrieved 2021-02-10.
   55. ^
       Link: mw-deduplicated-inline-style
       Tsai, Michael J. "Michael Tsai - Blog - UTF-8 String in Swift 5".
       Retrieved 2021-03-15. Switching to UTF-8 fulfills one of String’s
       long-term goals to enable high-performance processing, [..] also lays
       the groundwork for providing even more performant APIs in the future
   56. ^
       Link: mw-deduplicated-inline-style
       Mattip (2019-03-24). "PyPy Status Blog: PyPy v7.1 released; now uses
       utf-8 internally for unicode strings". PyPy Status Blog. Retrieved
       2020-11-21.
   57. ^
       Link: mw-deduplicated-inline-style
       "PEP 623 -- Remove wstr from Unicode". Python.org. Retrieved
       2020-11-21. Until we drop legacy Unicode object, it is very hard to
       try other Unicode implementation like UTF-8 based implementation in
       PyPy
   58. ^
       Link: mw-deduplicated-inline-style
       "/validate-charset (Validate for compatible characters)".
       docs.microsoft.com. Retrieved 2021-07-19. Visual Studio uses UTF-8 as
       the internal character encoding during conversion between the source
       character set and the execution character set.
   59. ^
       Link: mw-deduplicated-inline-style
       "/utf-8 (Set Source and Executable character sets to UTF-8)".
       docs.microsoft.com. Retrieved 2021-07-18.
   60. ^
       Link: mw-deduplicated-inline-style
       "absent std::u8string in C++11". NewbeDEV. Retrieved 2021-11-01.
   61. ^
       Link: mw-deduplicated-inline-style
       "Use the Windows UTF-8 code page - UWP applications".
       docs.microsoft.com. Retrieved 2020-06-06. As of Windows Version 1903
       (May 2019 Update), you can use the ActiveCodePage property in the
       appxmanifest for packaged apps, or the fusion manifest for unpackaged
       apps, to force a process to use UTF-8 as the process code page. [..]
       CP_ACP equates to CP_UTF8 only if running on Windows Version 1903 (May
       2019 Update) or above and the ActiveCodePage property described above
       is set to UTF-8. Otherwise, it honors the legacy system code page. We
       recommend using CP_UTF8 explicitly.
   62. ^
       Link: mw-deduplicated-inline-style
       "Appendix F. FSS-UTF / File System Safe UCS Transformation format"
       (PDF). The Unicode Standard 1.1. Archived (PDF) from the original on
       2016-06-07. Retrieved 2016-06-07.
   63. ^
       Link: mw-deduplicated-inline-style
       Whistler, Kenneth (2001-06-12). "FSS-UTF, UTF-2, UTF-8, and UTF-16".
       Archived from the original on 2016-06-07. Retrieved 2006-06-07.
   64. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       Pike, Rob (2003-04-30). "UTF-8 history". Retrieved 2012-09-07.
   65. ^
       Link: mw-deduplicated-inline-style
       Pike, Rob (2012-09-06). "UTF-8 turned 20 years old yesterday".
       Retrieved 2012-09-07.
   66. ^
       Link: mw-deduplicated-inline-style
       Alvestrand, Harald (January 1998). IETF Policy on Character Sets and
       Languages. doi:10.17487/RFC2277. BCP 18.
   67. ^ ISO/IEC 10646:2014 §9.1, 2014.
   68. ^ The Unicode Standard, Version 11.0 §3.9 D92, §3.10 D95, 2018.
   69. ^ Unicode Standard Annex #27: Unicode 3.1, 2001.
   70. ^ The Unicode Standard, Version 5.0 §3.9–§3.10 ch. 3, 2006.
   71. ^ The Unicode Standard, Version 6.0 §3.9 D92, §3.10 D95, 2010.
   72. ^
       Link: mw-deduplicated-inline-style
       McGowan, Rick (2011-12-19). "Compatibility Encoding Scheme for UTF-16:
       8-Bit (CESU-8)". Unicode Consortium. Unicode Technical Report #26.
   73. ^
       Link: mw-deduplicated-inline-style
       "Character Set Support". Oracle Database 19c Documentation, SQL
       Language Reference. Oracle Corporation.
   74. ^
       Link: mw-deduplicated-inline-style
       "Supporting Multilingual Databases with Unicode § Support for the
       Unicode Standard in Oracle Database". Database Globalization Support
       Guide. Oracle Corporation.
   75. ^
       Link: mw-deduplicated-inline-style
       "8.2.2.3. Character encodings". HTML 5.1 Standard. W3C.
   76. ^
       Link: mw-deduplicated-inline-style
       "8.2.2.3. Character encodings". HTML 5 Standard. W3C.
   77. ^
       Link: mw-deduplicated-inline-style
       "12.2.3.3 Character encodings". HTML Living Standard. WHATWG.
   78. ^
       Link: mw-deduplicated-inline-style
       "The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)". MySQL 8.0
       Reference Manual. Oracle Corporation.
   79. ^
       Link: mw-deduplicated-inline-style
       "Java SE documentation for Interface java.io.DataInput, subsection on
       Modified UTF-8". Oracle Corporation. 2015. Retrieved 2015-10-16.
   80. ^
       Link: mw-deduplicated-inline-style
       "The Java Virtual Machine Specification, section 4.4.7: "The
       CONSTANT_Utf8_info Structure"". Oracle Corporation. 2015. Retrieved
       2015-10-16.
   81. ^
       Link: mw-deduplicated-inline-style
       "Java Object Serialization Specification, chapter 6: Object
       Serialization Stream Protocol, section 2: Stream Elements". Oracle
       Corporation. 2010. Retrieved 2015-10-16.
   82. ^
       Link: mw-deduplicated-inline-style
       "Java Native Interface Specification, chapter 3: JNI Types and Data
       Structures, section: Modified UTF-8 Strings". Oracle Corporation.
       2015. Retrieved 2015-10-16.
   83. ^
       Link: mw-deduplicated-inline-style
       "The Java Virtual Machine Specification, section 4.4.7: "The
       CONSTANT_Utf8_info Structure"". Oracle Corporation. 2015. Retrieved
       2015-10-16.
   84. ^
       Link: mw-deduplicated-inline-style
       "ART and Dalvik". Android Open Source Project. Archived from the
       original on 2013-04-26. Retrieved 2013-04-09.
   85. ^
       Link: mw-deduplicated-inline-style
       "Tcler's Wiki: UTF-8 bit by bit (Revision 6)". 2009-04-25. Retrieved
       2009-05-22.
   86. ^
       Link: mw-deduplicated-inline-style
       Sapin, Simon (2016-03-11) [2014-09-25]. "The WTF-8 encoding". Archived
       from the original on 2016-05-24. Retrieved 2016-05-24.
   87. ^
       Link: mw-deduplicated-inline-style
       Sapin, Simon (2015-03-25) [2014-09-25]. "The WTF-8 encoding §
       Motivation". Archived from the original on 2016-05-24. Retrieved
       2020-08-26.
   88. ^
       Link: mw-deduplicated-inline-style
       "WTF-8.com". 2006-05-18. Retrieved 2016-06-21.
   89. ^
       Link: mw-deduplicated-inline-style
       Speer, Robyn (2015-05-21). "ftfy (fixes text for you) 4.0: changing
       less and fixing more". Archived from the original on 2015-05-30.
       Retrieved 2016-06-21.
   90. ^
       Link: mw-deduplicated-inline-style
       "WTF-8, a transformation format of code page 1252". Archived from the
       original on 2016-10-13. Retrieved 2016-10-12.
   91. ^
       Link: mw-deduplicated-inline-style
       "PEP 540 -- Add a new UTF-8 Mode". Python.org. Retrieved 2021-03-24.
   92. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       von Löwis, Martin (2009-04-22). "Non-decodable Bytes in System
       Character Interfaces". Python Software Foundation. PEP 383.
   93. ^
       Link: mw-deduplicated-inline-style
       "RTFM optu8to16(3), optu8to16vis(3)". www.mirbsd.org.
   94. ^ ^a ^b
       Link: mw-deduplicated-inline-style
       Davis, Mark; Suignard, Michel (2014). "3.7 Enabling Lossless
       Conversion". Unicode Security Considerations. Unicode Technical Report
       #36.

External linksEdit

     * Original UTF-8 paper (or pdf) for Plan 9 from Bell Labs
     * UTF-8 test pages:
          * Andreas Prilop Archived 2017-11-30 at the Wayback Machine
          * Jost Gippert
          * World Wide Web Consortium
     * Unix/Linux: UTF-8/Unicode FAQ, Linux Unicode HOWTO, UTF-8 and Gentoo
     * Characters, Symbols and the Unicode Miracle on YouTube
   Retrieved from
   "https://en.wikipedia.org/w/index.php?title=UTF-8&oldid=1082085332"
   Last edited on 11 April 2022, at 08:09
   Wikipedia
     * This page was last edited on 11 April 2022, at 08:09 (UTC).
     * Content is available under CC BY-SA 3.0 unless otherwise noted.
     * Privacy policy
     * About Wikipedia
     * Disclaimers
     * Contact Wikipedia
     * Terms of Use
     * Desktop
     * Developers
     * Statistics
     * Cookie statement
