[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] multiple encoding specs (Re: IE5.0 does not conform to RFC2376)
From: Chris Lilley <chris@w...> >An alternative method for achieving the same result is to use a filter >(this can be done in Apache and in Jigsaw) which automatically emits the >correct charset parameter based on reading the encoding declaration in >the XML instance. I think this is the approach that, ultimately, we all are hoping will be deployed. We are having a variant of this at our site: for when serving XHTML one must * make sure the HTML meta tag is correct (for HTML conformance) * make sure the XML encoding is correct (for XML conformance) * make sure the MIME charset is correct (for MIME conformance) Three chances to get something wrong! (And not forgetting that some HTML editors push the metatags or PI around, so you may end up with duplicated tags relating to character set inside the document.) Given that an XML processor may transcode the document without knowing the meanings of the elements (i.e., that the meta tag means something), the XML encoding has to have priority over the HTML meta tag value. And given that a proxies can transcode text/* files without knowing what kind of text it is (i.e., that it is XML, and so has a label), the MIME header has to have priority over the XML header PI. I think that is the logical order: generic operations must be allowed. However, it is all spoiled if there are systems which corrupt the labels: for example by rewriting the charset parameter incorrectly. It is far better to send the XML file without a charset parameter than to send it with a wrong one. >And if the charset parameter is present, then it should say the same >thing as the encoding declaration. The best way to ensure this is to >treat the XML encoding declaration as the prmary metadata resource and >to programatically derive the charset parameter from this; greater >robustness is at once achieved and also harmonisation of the MIME and >XML labelling. Yes, with the exception that the XML encoding PI could itself be derived from internal data (e.g. in XHTML). All of them need to be harmonized. The problem isn't really "which should have precedence?" (because all systems will break somewhere, given the state of webservers and current awareness) as much as it is "how can move the Web towards safety and interoperability, where the markup now available at each stage is made available to the next?" I think the current XML media types for MIME gives the appropriate policy for charset preference (transcodability is one property of text/* which application/* must not have), but, as Chris is pointing out, mechanisms to set the MIME charset parameter from XML (and to overwrite it on delivery too) have yet to be put into place. >However, I will point out that it is the consensus of the XML 1.0 >Recommendation that I am respecting - and that the RFC does not, by >altering the meaning of the default encoding. It could have been >harmionised with the XML REC; it was not. I think the XML SIG and WG pretty much all had concensus on the RFC at the end, in full knowledge of XML 1.0. But I think many of us came out of it thinking that it is safer to use application/xml. In particular, I think that a mismatch between the XML encoding declaration and the MIME charset (and the XHTML met tag) should some kind of weak Reportable User Error: people who don't want to accept transcoded text which has been mislabelled should have some kind of user option to report the error or abort. application/xml for safety text/xml for reach Rick Jelliffe Academia Sinica Computing Centre Taipei, Taiwan xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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