[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")
Eric Bréchemier a écrit : > Hello Philippe, > > On 9/21/07, Philippe Poulard wrote: >> Consider this declaration : >> <?kzy rapbqvat="EBG-13"?> >> >> The deecoded form of this declaration is : >> <?xml encoding="ROT-13"?> >> I can get it only if I test "ROT-13" on it ; althouh it is not strictly >> spoken an encoding, a parser that would support "ROT-13" would be able >> to decode it only if it test it or if it recognize the magic ASCII >> string "<?kzy" or whatever is the "guess" heuristic. >> > > I think you found an interesting example of ambiguous encoding, > falling in the category of "Character encodings such as UTF-7 that > make overloaded usage of ASCII-valued bytes" which "may fail to be > reliably detected." as mentioned in > http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info > > In this example, without external information, there is no way IMHO to > know for sure with limited input whether this is a ROT-13 encoding, or > an UTF-8 document starting with the "kzy" processing instruction. Yes, it is a special case in the special cases, as this silly encoding is fully-compatible with ASCII-based encodings ; the consequence is that a parser that doesn't know this encoding will parse correctly this document ; in the same way, you can specify <?xml encoding="UTF-8"?> whereas your document has been encoded in ISO-8859-1 ; if your document doesn't use àéèê characters and others out of the ASCII-7 bit, it will be decoded correctly Back to the ROT-13 example, a parser that support this encoding could try something before falling back to UTF-8 The tip for parsers is that when a strategy (BOM and others as specified in the spec., or some other hazardous heuristic) lead to <?xml encoding="XXX"?>, then XXX can be applied safely -- Cordialement, /// (. .) --------ooO--(_)--Ooo-------- | Philippe Poulard | ----------------------------- http://reflex.gforge.inria.fr/ Have the RefleX !
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