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SVG 1.2 Comment: Media type registration conformance and XML namespaces

From: L. David Baron <dbaron@dbaron.org>
Date: Mon, 1 Nov 2004 17:05:31 -0800
To: www-svg@w3.org
Message-ID: <20041102010531.GA4575@darby.dbaron.org>

The media type registration [1] for image/svg+xml should be changed so
that a conformant image/svg+xml processor must not treat XML elements
that are in no namespace as though they were in the SVG namespace.

Omission of namespaces seems to be a common authoring mistake in SVG on
the Web, for example [2], which suggests that this is a common mistake
in existing SVG implementations.  Such documents are not conformant SVG
documents because of:
 * the "an SVG namespace declaration must be provided" requirement in [3], and
 * because of the validity test in [5] (which would attempt to validate
   a document with no root element, since no elements are in the SVG
   namespace).

The SVG 1.1 specification does not define error handling for such
documents.  This is perfectly reasonable, since describing the behavior
of elements outside of the SVG namespace is out of scope of the SVG
specification.  However, now that the SVG specification contains a media
type registration, that media type registration should define how to
handle documents that would not otherwise be considered SVG when sent
using the registered media type.

I don't have strong opinions on *how* the registration should forbid
treating the no-namespace elements as SVG.  One reasonable way would be
stating that a conformant image/svg+xml processor must abort processing
of any document sent as image/svg+xml unless the root element of that
document is in the "http://www.w3.org/2000/svg" namespace.  I believe
this requirement would be sufficient to bootstrap the error-handling
requirements for unknown elements ([6] and [7]).

-David

[1] http://www.w3.org/TR/2004/WD-SVG12-20041027/mimereg.html

[2] http://www.w3.org/Consortium/Offices/Presentations/svgs/World.svg
    and the external resources it references:
      http://www.w3.org/Consortium/Offices/Presentations/svgs/WorldAS.svgz
      http://www.w3.org/Consortium/Offices/Presentations/svgs/WorldEU.svgz
      http://www.w3.org/Consortium/Offices/Presentations/svgs/WorldUS.svgz
    These four files currently use SVG elements with no namespace
    prefixes but have no xmlns attribute making the SVG namespace the
    default on the root element and have no DOCTYPE declaration that
    would introduce such an attribute.

[3] http://www.w3.org/TR/2003/REC-SVG11-20030114/struct.html#NewDocumentOverview
    (Although, for documents that have a DOCTYPE declaration, such as
    [4], it is unclear whether this requirement means that the xmlns
    declaration must also be explicitly provided.)

[4] http://www.w3.org/2002/05/memberGraph.svgz

[5] http://www.w3.org/TR/2003/REC-SVG11-20030114/conform.html#ConformingSVGDocuments

[6] http://www.w3.org/TR/2003/REC-SVG11-20030114/extend.html#PrivateData

[7] http://www.w3.org/TR/2003/REC-SVG11-20030114/implnote.html#ErrorProcessing

-- 
L. David Baron                                <URL: http://dbaron.org/ >

Received on Tuesday, 2 November 2004 01:06:05 UTC

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