![]() You will find that some editors (such as Notepad on Windows) will always add a BOM when you save a file with the UTF-8 encoding, others will offer you a choice. Most of the time you will not have to worry about the byte-order mark in UTF-8. ![]() In this situation, the BOM is often called a UTF-8 signature. However, the BOM may still occur in UTF-8 encoded text, either as a by-product of an encodingĬonversion or because it was added by an editor to flag the content as UTF-8. In the UTF-8 encoding, the presence of the BOM is not essential because, unlike the UTF-16 encodings, there is noĪlternative sequence of bytes in a character. ![]() The byte-order mark indicates which order is used, so that applications can immediately decode the content. You can see that the order of the two bytes that represent a single character is reversed for big endian vs. Each 2-digit hexadecimal number represents a byte in the stream of text. The picture below shows the bytes used in a sequence of two-byte characters. To communicate which byte order was in use, U+FEFF (the byte-order mark) was used at the start of the stream as a magic number that is not logically part of the text the stream represents. 16-bit code units can be expressed as bytes in two ways: the most significant byte first ( big-endian) or the least significant byte first ( little-endian). The BOM, when correctly used, is invisible.īefore UTF-8 was introduced in early 1993, the expected way for transferring Unicode text was using 16-bit code units using an encoding called UCS-2 which was later extended to UTF-16. With the introduction of U+2060 WORD JOINER, there's no longer a need to ever use U+FEFF for its ZWNSP effect, so from that point on, and with the availability of a formal alias, the name ZERO WIDTH NO-BREAK SPACE is no longer helpful, and we will use the alias here. The name BYTE ORDER MARK is an alias for the original character name ZERO WIDTH NO-BREAK SPACE (ZWNBSP).
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