#Add metadata with umark software
#Add metadata with umark code

UTF-8 is a sparse encoding in the sense that a large fraction of possible byte combinations do not result in valid UTF-8 text. Examples include programming languages that permit non- ASCII bytes in string literals but not at the start of the file.

#Add metadata with umark software

Not using a BOM allows text to be backwards-compatible with some software that is not Unicode-aware. The IETF recommends that if a protocol either (a) always uses UTF-8, or (b) has some other way to indicate what encoding is being used, then it 'SHOULD forbid use of U+FEFF as a signature.' An example of not following this recommendation is the IETF Syslog protocol which requires text to be in UTF-8 and also requires the BOM.

#Add metadata with umark code

The standard also does not recommend removing a BOM when it is there, so that round-tripping between encodings does not lose information, and so that code that relies on it continues to work. Byte order has no meaning in UTF-8, so its only use in UTF-8 is to signal at the start that the text stream is encoded in UTF-8, or that it was converted to UTF-8 from a stream that contained an optional BOM. The Unicode Standard permits the BOM in UTF-8, but does not require or recommend its use. The UTF-8 representation of the BOM is the ( hexadecimal) byte sequence 0圎F,0xBB,0xBF.

This allows U+FEFF to be used only as a BOM. In Unicode 3.2, this usage is deprecated in favor of the ' Word Joiner' character, U+2060. If the BOM character appears in the middle of a data stream, Unicode says it should be interpreted as a ' zero-width non-breaking space' (inhibits line-breaking between word-glyphs). This use of the BOM character is called a 'Unicode signature'. Therefore, placing an encoded BOM at the start of a text stream can indicate that the text is Unicode and identify the encoding scheme used. The byte sequence of the BOM differs per Unicode encoding (including ones outside the Unicode standard such as UTF-7, see table below), and none of the sequences is likely to appear at the start of text streams stored in other encodings. Generally the receiving computer will swap the bytes to its own endianness, if necessary, and would no longer need the BOM for processing. Hence, the process accessing the text can examine these first few bytes to determine the endianness, without requiring some contract or metadata outside of the text stream itself. The BOM is encoded in the same scheme as the rest of the document and becomes a noncharacter Unicode code point if its bytes are swapped. For the 16- and 32-bit representations, a computer receiving text from arbitrary sources needs to know which byte order the integers are encoded in. Unicode can be encoded in units of 8-bit, 16-bit, or 32-bit integers. Its presence interferes with the use of UTF-8 by software that does not expect non-ASCII bytes at the start of a file but that could otherwise handle the text stream.

Which Unicode character encoding is used.īOM use is optional.

The fact that the text stream's encoding is Unicode, to a high level of confidence.

The byte order, or endianness, of the text stream in the cases of 16-bit and 32-bit encodings.The byte order mark ( BOM) is a particular usage of the special Unicode character, U+FEFF BYTE ORDER MARK, whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text: For the name of U+FEFF in Unicode and the alternative usage as a zero-width non-breaking space, see Word joiner. For the program used in X-ray absorption spectroscopy, see FEFF (software). For the airport in Central African Republic with the airport code FEFF, see Bangui M'Poko International Airport.