Manuel Mall wrote:
Extensions specific to a particular renderer and / or extensions which
constitute a rendering hint (e.g. render this image as a grayscale)
should be in a renderer specific namespace.
-0.5. I would be more comfortable with the idea of renderer-specific
formatting objects and properties if the XSL specification had some
itself, but so far the XSL SG has (strictly) avoided defining any. I am
unaware of the commercial implementations going in this direction either.
As far as the XSL specification is concerned, while some FO's/properties
are defined for printed paper only, some for hearing only, and some for
screen output only (fo:multi-switch for example), nothing is defined
with respect to a specific renderer. I would think, then, with a little
more effort the fox extensions created could likewise be done
generically, without respect to specific renderers but just to the type
of output: aural/paper/screen, etc.
Even if the same type of rendering hint can be used by different
renderers they still should be in separate namespaces as this allows
the user control over behaviour on a per renderer basis without
changing the fo file.
I think what you're saying here defeats the purpose of XSL: it is a
specification for a document that is *independent* of the renderer type.
You may be opening up a can of worms, if for the same XSL document,
properties exist that would result in, say, a PDF document having a red
background and a PCL document having a blue background. This has never
been the goal of XSL.
[Also, I think you'll be opening up a *barrel* of worms, if, in having
renderer-specific *extension* properties, we now need to override
regular XSL namespace properties just for the sake of providing
renderer-specific styling. (E.g., instead of font-size, now we have
pdf:font-size, pcl:font-size, etc., etc.) After all, it would not be
just for FOP's *extension* FO's/properties that renderer-specific
styling might be wanted, and if the goal is allow for different styling
based on the renderer without needing to change the fo file, eventually
you will have to override the fo: properties in addition to the fox: ones.]
If a user has a stylesheet that needs a little bit of tweaking between
two different renderers, I think the main solution is to have the user's
xslt handle that, perhaps by having the user pass in an xsl:param
holding the renderer type, and then use xsl:choose, xsl:if,
xsl:attribute, etc. with that param value to change the formatting
objects/properties based on the renderer.
For example lets assume we want to support image
conversion hints which allows tuning of the image output format.
Instead of having <fo:external-graphic
fox:output-conversion="grayscale" src="xyz.png" /> I would recommend to
use render specific hints like <fo:external-graphic
afp:output-conversion="grayscale" pcl:output-conversion="bitmap"
pdf:output-converion="jpeg" src="xyz.png" />.
But what if you always want grayscale, independent of formatter? In
your example above, you would need to duplicate this same value three
times (afp:, pcl:, pdf:) instead of just once (fox:).
Also, what if you choose another renderer outside of afp/pcl/pdf? The
grayscale would not be activated with a renderer outside your explicitly
given list. In this way you end up losing the "future-proofing" of the
document that is another desired aspect of XSL.
But, one way around these two concerns is to still allow a fox:property
wherever you would allow a pcl:property, afp:property, etc. The value
of fox:property would be used whereever a renderer-specific value was
not specified.
This may not be a good
example but I hope it illustrates what I am trying to achieve.
No, it was an excellent example for discussion.
Glen
