SVG12: charset parameter for image/svg+xml
Boris Zbarsky
bzbarsky at MIT.EDU
Mon Nov 1 21:46:15 CET 2004
Chris Lilley wrote:
> On the contrary! The +xml convention clearly indicates, for an unknown
> media type, that it is xml; thus, that an XML processor should be used;
> which will correctly determine the encoding from the xml encoding
> declaration or lack therof.
I think the concern was about what happens when someone sends the
following HTTP header:
Content-Type: image/svg+xml; charset=iso-8859-1
combined with an XML document that has no encoding declaration (so
defaulting to UTF-8).
Now per the type registration for "image/svg+xml", the above
Content-Type header is invalid, right? So what's a UA to do? What
encoding to use? Using UTF-8 means hardcoding knowledge about the fact
that image/svg+xml, unlike most other character-based types used today,
doesn't have a charset parameter.
> No, they would not. RFC 3023 already allows the charset to be omitted,
> and gives rules to follow for this case. SVG follows those rules, as the
> registration document makes plain.
The problems arise when there IS a charset parameter. I don't think
anyone ever claimed there is a problem when the charset parameter is
omitted.
> In general, a representation provider SHOULD NOT specify the
> character encoding for XML data in protocol headers since the data is
> self-describing
Given that this is a not a MUST NOT, people will continue to do this in
some cases (particularly as some web servers automatically tack on a
"charset" parameter to Content-Type headers).
-Boris
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