transclusion and xpointer [was: [docbook-tc] DocBook Technical Committee Meeting Minutes: 15 July 2009]

["Grosso, Paul" <pgrosso@ptc.com>]

> 9b.  RFE 2820947 "Ability to transclude text".
> 
> First we discussed conref since the requestor mentioned it.
> Gershon and Paul described problems with implementing
> conref, including hard coding references. Gershon suggested
> that DITA's keyref, which uses a level of indirection,
> would be more flexible.  A note from Eliot Kimber
> didn't reach the list in time, so it will be reviewed
> for the next meeting.
> 
> Paul: use existing standards such as XInclude with xpointer.
> Creating new schemes is a whole big thing.
> 
> Bob: the xpointer scheme is not a standard, so there is no way
> to include all the children of an element without including
> the element itself.  That can help with the problem of duplicate
> ids when importing the same content more than once.

> Norm: perhaps we could define some small subset of
> xpointer scheme.

Speaking about XPointer can be tricky just due to the
vocabulary (to say nothing of the technology).  Best not
to say "xpointer" unqualified because someone is certain
to misunderstand.

There are three W3C XPointer Recommendations:

* XPointer Framework
  http://www.w3.org/TR/xptr-framework/

* XPointer element() scheme
  http://www.w3.org/TR/xptr-element/

* XPointer xmlns() scheme
  http://www.w3.org/TR/xptr-xmlns/

These three allow referencing any single element in a document
(but not multiple elements and not sub-element content).

A registry of XPointer schemes is maintained at
http://www.w3.org/2005/04/xpointer-schemes/
This includes (but only as "one being reviewed") the xpointer()
scheme.  It's hard to say how widely the schemes mentioned there 
are supported, but it would probably be better to pick one of the
more supported of them that addresses our needs (perhaps xpath1)
than to invent our own.

Then there is the W3C XInclude Recommendation:
http://www.w3.org/TR/xinclude/

It defines an xi:xinclude element with an xpointer attribute
whose value is a valid xpointer expression.  The XInclude spec
mandates support for XPointer Framework and XPointer element() 
scheme and allows for support of other XPointer schemes.  

paul