Re: XML5

[Henri Sivonen <hsivonen@iki.fi>]

On Dec 16, 2010, at 00:17, Dave Pawson wrote:

> On Wed, 15 Dec 2010 20:24:35 -0800
> Henri Sivonen <hsivonen@iki.fi> wrote:
> 
>> ... thought it's not clear if
>> it's that worthwhile to make XML more suitable for the Web now that
>> SVG and MathML work in text/html.
> 
> Read simply, that seems a strange thing to say Henri?
> Would you expand please.

There are four Web language vocabularies: (X)HTML, SVG, MathML and ARIA. XBL2 is on track to become a 5th. XSLT is kinda there on the side, but you don't put XSLT elements into a document tree that gets rendered in a browsing context. (XUL and XBL1 never got implemented by more than one browser engine and will no longer be available for use by random Web sites in Firefox 4.)

Prior to the HTML5 parsing algorithm, only HTML+ARIA worked in text/html, so you got more vocabulary by using XML. Now that SVG and MathML work in text/html, you don't get more vocabulary by using XML. Using text/html buys you the ability to hack SVG and MathML output into your pre-existing text/html-oriented software (taking an existing CMS and bullet-proofing it to always emit well-formed XML is *hard*) and more graceful degradation in IE < 9. Using XML buys you the ability to avoid taking an HTML serializer off the shelf and the risk for the YSoD. 

You still get XSLT through <?xml-stylesheet?> if you use XML but not if you use text/html. (Note that you can pass an HTML parser-generated DOM to XSLTProcessor.) However, even if from point of view of this mailing list XSLT is a central feature, on the Web scale it is a fringe feature (but still used just enough that Opera and WebKit were dragged into implementing it not because they particularly wanted to but in order to be able to render sites that IE and Firefox are able to render). The masses of Web authors will care more about being able to do SVG in text/html than about not being able to do <?xml-stylesheet?> in text/html.

You get more proprietary extensibility with XML (which lets enterprise vendors say they do XML to appear to use a standard while they lock the customer in on the vocabulary level). However, people really shouldn't be sending content using proprietary vocabularies on the Web. Even if you style it with CSS to present it, the browser won't know its semantics and can't expose the content properly to assistive technologies for example.

Home-grown vocabularies are used over XHR, but for these kind of cases, JSON is being used more and more.

So when the vocabularies that browsers have built-in awareness for (in the sense of using them in document trees that are displayed in a browsing context) now work in text/html, a big reason to use XML is removed. This leaves less reason to use XML on the Web, which makes it less worthwhile to make XML more suitable for use on the Web.

-- 
Henri Sivonen
hsivonen@iki.fi
http://hsivonen.iki.fi/