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Re: SVG12: data: default type (and a top-level type for fonts)

From: Chris Lilley <chris@w3.org>
Date: Thu, 20 Oct 2005 22:15:31 +0200
Message-ID: <428778024.20051020221531@w3.org>
To: Bjoern Hoehrmann <derhoermi@gmx.net>
Cc: www-svg@w3.org, David Singer <singer@apple.com>

On Sunday, April 24, 2005, 7:27:43 PM, Bjoern wrote:

BH> Dear Scalable Vector Graphics Working Group,

BH>   http://www.w3.org/TR/2005/WD-SVGMobile12-20050413/ is unclear about
BH> proper syntax for the 'data:' URL scheme,

While sympathetic to your concern regarding implementations as
articulated below, lets take this one step at a time.

SVGT1.2 says that the syntax is defined by RFC 2397, which is a normative
reference:

[RFC2397]
    'The "data" URL scheme', L. Masinter, August 1998.
    Available at http://www.ietf.org/rfc/rfc2397.txt.

That RFC says

       dataurl    := "data:" [ mediatype ] [ ";base64" ] "," data
       mediatype  := [ type "/" subtype ] *( ";" parameter )
       data       := *urlchar
       parameter  := attribute "=" value

and

   If <mediatype> is omitted, it
   defaults to text/plain;charset=US-ASCII.

Thus, we believe that the specification is in fact crystal clear
regarding the exact syntax.

BH> many SVG tools fail to specify
BH> a proper media type for the data

Yes, they do. Please complain to the producers of such tools.

BH>  in which case the scheme defaults to
BH> text/plain;charset=us-ascii which is hardly ever intended for resources
BH> included in SVG documents.

Agreed, although with a caveat - there is no Media Type for fonts,
despite several attempts to create such a thing - ages ago by myself,
and more recently by Dave Singer with
http://www.ietf.org/internet-drafts/draft-singer-font-mime-00.txt
except its now expired:
http://www.ietf.org/internet-drafts/draft-singer-font-mime-01.txt

I copied Dave Singer on this message.

I suppose that even so, something like x-font/x-opentype or
application/vnd.whoever.fonttype could be used.

BH>  http://www.w3.org/2004/10/RecsFigure.svg is
BH> an example for this.

That example is not in our specification. Please complain to the tool
vendor (Adobe) and also to the IESG for not allowing a font/* top-level
type.

BH> Please change the draft such that it is very clear to authors and
BH> authoring tool developers that this is not acceptable and that
BH> conforming user agents must not assume any other media type in this
BH> case.

I checked and there are no examples of data: URIs in our spec with
incorrect media types, and the specification is quite clear on the
subject.

We find that there is indeed something of a problem with font Media
Types, but that problem is not on our specification and it is not clear
what we can do about it.

In sum, focusing here on the actual specification, we find that there
is nothing to change in this regard.

-- 
 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Thursday, 20 October 2005 20:16:16 GMT

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