[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: [Summary] Why is Encoding Metadata (e.g. encoding="UTF-8")
Rudick, Tom a écrit : > If the HTTP headers do not indicate what the encoding of the document > is, you must read the document (at least the first line) and figure out > what the encoding is. However, how is this accomplished? If you don't > know the encoding of the document to begin with, how can you read even > the first line? > > After reading this http://www.w3.org/TR/REC-xml/#sec-guessing, it seems > that instead of reading what <?xml encoding="utf-8"?> has to say, > parsers simply look at the first few octets of the document and compare > it to several known encodings of the text <?xml. Then, they just > continue to read the rest of the document. Not exactly : the first few octets will indicate if <?xml encoding="blah-blah"?> is coded on 1, 2, or even 4 bytes (for UCS) ; the charset of the sequence <?xml encoding="blah-blah"?> is limited to ASCII-7 bits, which is fortunately compatible with UTF-8, ISO-8859-1 and some others, and easily decodable if coded on 2 or 4 bytes, because the same sequence is mapped to ASCII-7 bits, whatever the number of bytes (zero-extension) ; for example : Bits Encoding Hex Dec Char 7 US-ASCII 41 65 A 1000001 8 ASCII 8bits 41 65 A 01000001 16 UCS-2 41 65 A 00000000 01000001 32 UCS-4 41 65 A 00000000 00000000 00000000 01000001 So, the encoding can be read (if any) I guess some parsers have additional heuristics for reading successfully the sequence <?xml encoding="blah-blah"?> ; maybe some try-catch to apply with the set of charset they know ? -- Cordialement, /// (. .) --------ooO--(_)--Ooo-------- | Philippe Poulard | ----------------------------- http://reflex.gforge.inria.fr/ Have the RefleX !
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