Editing UTF-8 (section)

=== Byte-order mark ===
If the Unicode [[byte-order mark]] {{tt|U+FEFF}} is at the start of a UTF-8 file, the first three bytes will be {{mono|0xEF}}, {{mono|0xBB}}, {{mono|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.<ref>{{citation | chapter-url = https://www.unicode.org/versions/Unicode15.0.0/ch02.pdf | title = The Unicode Standard&nbsp;— Version 15.0.0 | chapter = Chapter 2 | page = 39 }}</ref> 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 literal]]s 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).<ref>{{Cite web |title=UTF-8 and Unicode FAQ for Unix/Linux |url=https://www.cl.cam.ac.uk/~mgk25/unicode.html}}</ref>