The future of XML related technologies in Mozilla

After implementing xml:id/setIdAttr* and getting somewhat expected 
critical comments about adding new bloat I started to wonder what are
the "new" XML technologies that should be or could be supported in Mozilla.




Currently implemented, not in wide use:

XPointer is in xmlextras, but is it used by anyone?

XML Events is used only by XForms, though some external project(s) use
it too. XML Events could be implemented as an extension, if XTF 
supported extensions for attributes. (There is bug and patch for XTF 
attributes). Installing yet another extension would be an annoyance for 
users, but perhaps this situation could be worked out with better 
extension dependencies handling.

xml:base is implemented, but does anyone really use it?

XLink is partially implemented and iirc used in SVG, and
there is a patch to fix some of its problems and reduce the
extra size overhead it currently adds to all xml element objects.

MathML shouldn't perhaps be mentioned here, but it is something which is
implemented but not used too often.




Possible new features:

xml:id. Bug and patch available. Opera supports this. Useful in DIY
languages (no need to use DTDs).

XInclude. Could this be more useful in application development than in
web pages. Something to complement XUL overlays?

SMIL (animation module). This is a big one, but for SVG animations and
perhaps for XUL UI animations too. There is or was a partial patch 
somewhere.

XBL2 ;)

DOM Level 3: Core, Load&Save (these are already partially implemented)

What else... validation?...




So the questions I have is that although I'd like to reduce the binary
size, these all add some overhead or bloat - so in which cases that is
acceptable. What are the features we really need and why? Who/what is
the target audience/user for these technologies; web developers, xul
app developers, researchers, firefox UI, extension developers, 
implementators of new XML based languages?

Can we somehow measure the need for a feature and say that it is ok to
implement it if the binary size increases only XXkB. Or that if code is 
removed elsewhere, new features can be implemented.
(Performance regressions aren't ever acceptable, IMHO)




I think Mozilla's support for XML technologies should evolve and maybe 
we shouldn't always think only web developers. HTML5 doesn't solve all
the problems ;)



br,


-Olli