[whatwg] Allow Select SVG Elements In <head>

Mon Dec 6 18:35:15 PST 2010

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).

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
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