Unicode and HTML: Difference between revisions

Revision as of 23:49, 26 February 2013

Revision as of 04:48, 9 June 2013

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===Byte order mark/Unicode sniffing===

For both serializations of HTML (content-type "text/html" and content/type "application/xhtml+xml"), the Byte order mark (BOM) is an effective way to transmit encoding information within an HTML document. For UTF-8, the BOM is optional, while it is a must for the UTF-16 and the UTF-32 encodings. (Note: UTF-16 and UTF-32 without the BOM are formally known under different names, they are different encodings, and thus needs some form of encoding declaration – see [[UTF-16BE]], [[UTF-16LE]], [[UTF-32LE]] and [[UTF-32BE]].) The use of the BOM character (U+FEFF) means that the encoding automatically declares itself to any processing application. Processing applications need only look for an initial 0x0000FEFF, 0xFEFF or 0xEFBBBF in the byte steamstream to identify the document as UTF-32, UTF-16 or UTF-8 encoded respectively. No additional metadata mechanisms are required for these encodings since the byte-order mark includes all of the information necessary for processing applications. In most circumstances the byte-order mark character is handled by editing applications separately from the other characters so there is little risk of an author removing or otherwise changing the byte order mark to indicate the wrong encoding (as can happen when the encoding is declared in English/Latin script). If the document lacks a byte-order mark, the fact that the first non-blank printable character in an HTML document is supposed to be "<" (U+003C) can be used to determine a UTF-8/UTF-16/UTF-32 encoding.

===Encoding overriding===