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Re: from-page-master-region() and Re: reference-orientation

From: Peter B. West <lists@pbw.id.au>
Date: Wed, 31 May 2006 08:01:05 +0100
Message-ID: <447D3F31.9040200@pbw.id.au>
To: xsl-editors <xsl-editors@w3.org>

>  
> The XSL FO SG discussed this issue again at our recent f2f.
> 
> We reconfirmed our position on this issue which is that there 
> will be no change to the 1.1 spec in this area.
> 
> We understand that there are two ways inheritance could work 
> in the FO tree with respect to the properties in the layout-master-set. 
> Each of the two ways is necessary to support certain capabilities. 
> In scoping XSL 1.0, we decided to restrict ourselves to a single 
> simple inheritance model that always follows the structure of the 
> formatting object tree (section 5.1.4); that limitation continues 
> in XSL 1.1. We have always had plans to allow the other way as part 
> of a larger effort to support layout-driven composition requirements, 
> but we determined that work to be out of scope for 1.0. The reasons 
> we picked the inheritance model we did instead of the other one are: 
> (1) we had to choose one for 1.0, and most of the time one wants 
> inheritance from the content, and (2) though out of scope for 1.0, 
> we knew we would want to do layout-driven formatting at some point, 
> and this would require much more capability to "inherit" properties 
> in ways other than down the formatting object tree, so we decided 
> we'd leave all such capabilities for the future work.
> 

My thanks to the editors for their valiant, if unsuccessful, attempts to
enlighten me as to the meaning of "a single simple inheritance model
that always follows the structure of the formatting object tree."

Clearly I have been at cross purposes with the editors in arguing for
what I understood to be "a single simple inheritance model that always
follows the structure of the formatting object tree,"  because, all the
while, I thought that the changes proposed would destroy such a model.

Alas, I am still not entirely sure of the principles.  I look at this
familiar diagram -
http://www.w3.org/TR/xsl/slice6.html#section-N10230-Pagination-Tree-Structure
- and I cannot quite see how it works.

As best I can determine, the regions of the simple-page-master, on the
left of the great divide, inherit two properties and two properties
only, viz. writing-mode and reference-orientation, from page-sequence on
the right. This appears to be a form of cul-de-sac inheritance because,
as near as I can determine from the editors' excellent exposition of the
rationale, the simple-page-master and its regions create no further
ripples on the inheritance of flows and static-contents, which inherit
everything else in the usual uncontroversial manner.

Pondering this mysterious effect, and considering another popular
diagram from the Recommendation, to wit
http://www.w3.org/TR/xsl/slice4.html#area-tree-sample
I am beginning to suspect that there are undocumented quantum mechanical
effects at work.

I the above diagram, flows areas are pendant to areas from the
troublesome regions. Now, as I have recently been reminded by the
editors, area traits don't inherit.  However, it would be extremely
convenient if superpositions of the property "writing-mode" and the
trait "writing-mode", and like-wise for "reference-orientation", were
introduced. These superpositions could be collapsed into one state or
the other as required from moment to moment during the reading of the
Recommendation; a Heisentrait, so to speak, or Schrödinger's attribute.

At the sub-atomic level, of course, this is all very simple, but it can
be difficult to follow with the logic of macroscopic structures. It may
surprise the editors to learn that many readers, and indeed
implementors, lack even a rudimentary understanding of quantum
mechanics.  Witness my own misunderstandings of this change. At the very
least the principles deserve a non-normative appendix.

My congratulations on this ground-breaking work.

Peter West


-- 
Peter B. West <http://cv.pbw.id.au/>
Folio <http://defoe.sourceforge.net/folio/>
Received on Wednesday, 31 May 2006 07:01:28 GMT

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