[whatwg] Fwd: Allow Select SVG Elements In <head>

Thu Dec 22 04:28:00 PST 2011

Cameron McCormack forwarded this proposal to public-svg-wg a year ago
(thanks, Cameron!) but no one commented on it, so I'm reposting it
here. Is this something the SVG WG is willing to do?

Thanks!
-Hugh

---------- Forwarded message ----------
From: Ian Hickson <ian at hixie.ch>
Date: Mon, Dec 6, 2010 at 9:35 PM
Subject: Re: [whatwg] Allow Select SVG Elements In <head>
To: Hugh Guiney <hugh.guiney at gmail.com>
Cc: whatwg <whatwg at whatwg.org>

On Fri, 27 Aug 2010, Hugh Guiney wrote:
>
> I'm authoring an XHTML host document with namespaced inline SVG and
> XLink. I have vector images that recur throughout the site. I'd like to
> implement SVG's <defs> and <use> to reduce the file size of the document
> and keep style separate from content, as with CSS.
>
> If I put an SVG tree with <defs> anywhere in the XHTML document, other
> trees with <use xlink:href> will correctly reference it, as tested in
> the latest public release Gecko, Webkit, and Opera. So the question
> becomes, where do I put it? The most obvious answer seems to be <head>,
> since, like CSS definitions, this is metadata being defined for use
> elsewhere in the document. The only problem is, Validator.nu doesn't
> like it:
>
> "Error: SVG element svg not allowed as child of XHTML element head in
> this context. (Suppressing further errors from this subtree.)"
>
> Same error when ditching the root <svg> and including only <defs>, the
> result of which still works in all but Opera.
>
> This error can be avoided if the <defs> tree is put in the XHTML <body>,
> but then there is blank space the size of the defined shapes at the top
> of the document in all 3 engines. A workaround is to give <svg> a @width
> and @height both of 0. But leaving the definitions in the <body> when
> they technically don't represent contextual content strikes me as
> non-semantic.
>
> My proposition would be to simply spec a subset of SVG consisting only
> of metadata elements as valid in HTML's <head> context. This could be
> just <defs>—I'm unsure if there are any other elements that fit this
> definition since I am relatively new to SVG; but in either case it'd aid
> semantics and is already supported in today's SVG-capable browsers.

This is an interesting idea. I would recommend approaching the SVG working
group and suggesting that they define the content model of <svg> and other
SVG elements such that there's two ways to use it: one where <svg> is
considered embedded content, and one where it's considered metadata
content, with appropriate restrictions on the latter. With such a set of
definitions in place, the HTML spec's model would just work (it already
refers to the content model of <head> as just "metadata content", for
instance).

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