In general, these issues are fading away as people adopt newer versions of browsers and editing tools.
What follows are some situations where the byte-order mark has been known to cause problems. You can also specify in your preferences (see illustration) whether new documents should use a BOM by default. For example, if you use Save As in Dreamweaver and your file has a BOM at the start you will see a check mark in the box labeled 'Include Unicode Signature (BOM)'. With the Latin 1 (ISO 8859-1) character encoding, the signature displays as characters .Īlternatively, your editor may tell you in a status bar or a menu what encoding your file is in, including information about the These are the bytes that compose BOM represented as the characters those bytes represent in that encoding. If your editor or browser applies the wrong character encoding to a UTF-8 encoded file with a BOM, you are likely to see a sequence of bytes at the start of the file. A BOM that is included in the page lower down (typically due to content being added to the page from an external source) will be reported in the Detailed Report section. A BOM at the start of the page will be reported in the Information panel. You can find out whether a page contains a BOM at the start or further down in the content by using the W3C Internationalization Checker. If you use a UTF-16 encoding for your page (and we strongly recommend that you don't), there are some additional considerations. See the section below for more information about those. However, bear in mind that it is always a good idea to declare the encoding of your page using the meta element, in addition to the BOM, so that the encoding is apparent to people looking at the source text.Īlso there are a number of situations where the BOM, particularly because it is invisible, may cause a problem. The UTF-8 BOM offers reliable encoding detection, since it is extremely short and stable, works in XML and HTML, and works whether your page is read over the network or not (unlike HTTP declarations). In HTML5 browsers are required to recognize the UTF-8 BOM and use it to detect the encoding of the page, and recent versions of major browsers handle the BOM as expected when used for UTF-8 encoded pages.
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.
BB EDITOR FOR MAC CODE
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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