What is happening with XBL?

[ Bcc: set to: public-forms@w3.org ; please set Reply-To: to just 
public-webapps@w3.org ]

XBL Fans,

In case you missed it, about a week ago, Anne van Kesteren wrote a nice 
blog about some of the recent activities with XBL including pointers to 
some related work by Dimitri Glazkov (e.g. Use Cases). Given AvK's blog 
is short-ish, I'll quote it here:

[[
http://annevankesteren.nl/2011/01/xbl

What is happening with XBL?
15th January 2011


    What is happening with XBL?

<http://annevankesteren.nl/2011/>

Despite quite a bit of interest when XBL 2.0 
<http://www.w3.org/TR/2007/CR-xbl-20070316/> was developed it has not 
made it into browsers thus far. Perhaps because Jonas Sicking is too 
occupied, or perhaps it simply is too complex. The drive for XBL started 
moving again late last year when Ian Hickson simplified 
<http://lists.w3.org/Archives/Public/public-webapps/2010JulSep/0675.html> the 
specification. Instead of a new language XBL would become a set of 
extensions to HTML.

In parallel, Dimitry Glazkov started drafting Component Model Use Cases 
<http://wiki.whatwg.org/wiki/Component_Model_Use_Cases>, a WHATWG Wiki 
document anyone can contribute to. Effectively taking a fresh look at 
what we want nowadays from XBL. He also wrote a great post for anyone 
not familiar with the types of scenarios XBL will tackle: What the Heck 
is Shadow DOM? 
<http://glazkov.com/2011/01/14/what-the-heck-is-shadow-dom/> It is a 
complex subject, but the way he conveys it makes it look easy.

Now I have been hopeful for XBL happening pretty much since we started 
working on HTML5 in 2004 so I am not too excited yet. But for the first 
time in almost four years we are making progress again.

]]

I think there are at least four different versions of XBL specs with 
various levels of implementations:

1. Mozilla XBL: original, Mozilla-specific; Blue Griffon. Perhaps some 
XForms implementations also implement Mozilla XBL?

2. sXBL: first attempt at a standard XBL, aimed mainly at SVG. Lots of 
interest at SVG Open three or four years ago but apparently interest has 
died?

3. XBL2 CR: - some XForms implementations reported; Jonas announced some 
work (last report May 2010)

   http://www.w3.org/TR/2007/CR-xbl-20070316/
   
http://lists.w3.org/Archives/Public/public-webapps/2010JulSep/1008.html   [from 
Leigh]
   
http://lists.w3.org/Archives/Public/public-webapps/2010AprJun/0485.html 
[from Jonas]

4. XBL2-cutdown: Hixie's September 2010 version. Not clear if there is 
any implementers support for this enough or if any 
prototyping/implementing has been done.

   http://dev.w3.org/2006/xbl2/
   http://lists.w3.org/Archives/Public/public-webapps/2010JulSep/0675.html

It would be useful to get updated implementation plans/data, especially 
for #3 and #4 above.

As Anne implies, Dimitri's work raises questions about whether XBL2 CR 
or XBL2-cutdown are the right approach or is a different approach is 
needed?

Additionally, given the broad set of constituencies here, and the 
requirement to preserve implementation investment, is it realistic to 
expect one spec to satisfy all of the use cases and requirements?

-Art Barstow