Re: DSSSL extensions for XSL

Subject: Re: DSSSL extensions for XSL
From: James Clark <jjc@xxxxxxxxxx>
Date: Mon, 29 Sep 1997 12:15:08 +0700
Paul Prescod wrote:
> > > Flow object macros seem like they will be very nice syntactically. Can
> > > the flow object macro inspect the inherited characteristics in contexts
> > > other than characteristic specifications or do we still have to wait for
> > > first class modes for that??
> >
> > The inherited characteristics are packaged up into a style object and
> > there's no way at the moment to look inside style objects.  First-class
> > modes wouldn't help with that.
> I realized I hadn't said that clearly when I sent that. I meant that if
> you could inspect style objects then you could pass arbitrary
> information down the flow object tree in characteristics and retrieve
> them in flow object macros by inspecting the style object. But since
> this is not possible, we will have to wait for first class modes to pass
> information down the flow object tree to be used outside of
> characteristic expressions.

I realized I had probably missed the point of your question a few
minutes after sending my reply.  After thinking about this a bit more,
I've realized there's a flaw in the current design: it doesn't work when
you use actual-c or inherited-c in the specification of a non-inherited
characteristic on a flow object macro, because there is no flow object
with respect to which these characteristics can be evaluated. So I've
now got rid of the #!inherited business; instead the inherited
characteristics are all automatically applied to a sequence flow object
that is wrapped around what is created by the body of the flow object
macro.  The upside is that you can now use inherited-c and actual-c in
the body of the flow object macro, and they will give the same result as
if they were used in a characteristic on the invocation of the flow
object macro.

> Will first class flow objects provide a mechanism for *returning* data
> up the execution context tree?

Do you mean first class modes rather than first class flow objects? If
so, the answer is no.  The principle that a construction rule returns a
sosofo that is a black box to the expression language is critical to
implementing DSSSL efficiently (for Jade at least).


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