W3C home > Mailing lists > Public > www-style@w3.org > December 2002

XBL is (mostly) W3C redundant, and CSS is wrong W3C layer for semantic behavior *markup*

From: Shelby Moore <shelby@coolpage.com>
Date: Sun, 22 Dec 2002 17:04:09 -0600
Message-Id: <4.1.20021222145808.01873510(null)>
To: www-style@w3.org
Cc: Ray Whitmer DOM Chair <rayw@netscape.com>, Peter Trudelle Mgr XFPE <trudelle@netscape.com>

Before responding on this thread, I beg the reader to also read *entirely* the
linked references and threads.

My high level semantic (not my complete) summary understanding is that XBL is
used to abstract extensible semantic (by meaning) content markup from the
implementation and style.  In content markup, we merely declare, "Widget", and
XBL binds the abstract content markup to the widget's implementation details. 
XBL also provides for reuse of widgets in other widgets:

http://www.w3.org/TR/xbl/

XBL was submitted to W3C, by AOL on behalf of itself and mozilla.org:

http://www.w3.org/Submission/2001/05/

The W3C team, apparently with Bert Bos of CSS WG listed as editor, has already
commented that XBL is "complex", depends on many format layers (i.e. may
undermine layer modularity), "recursive" in yet not fully explored ways,
"powerful" possibly beyond the primary goals (see Tim Berners-Lee's "principle
of least power"...we all know he "created" the world wide web), depends on
"procedural code" (i.e. does not optimally modularize or abstract the
procedural binding layer), and mentioned other possible solutions:

http://www.w3.org/Submission/2001/05/Comment

I wish to add two comments:

1. XBL is (mostly) W3C redundant

2. CSS is wrong W3C layer for semantic behavior *markup*


As W3C Team commented, the templating portions of XBL could be accomplished
with XSLT, an existing, widely implemented W3C standard.  The advantage of
using XSLT is that the binding of the content markup abstraction does not
involve the CSS layer.  Content markup abstraction (model) should not depend on
a controller layer (CSS).  If you mix the two layers, then you destroy the
benefits of orthogonality (modularity) in the "model-controller" design model. 
An example of such a benefit is exchangeability of CSS, i.e. if content markup
depends on a style sheet, then the style sheet is required and thus no longer
exchangeable.

Using XSLT for templating does have the attribute that is just a transformation
layer and thus the DOM will have no concept of the original content markup
abstractions-- only the templated output.  However, this may be desireable, for
the same type of reasoning of orthogonality.  The DOM is not designed to be the
same layer as abstract content markup.  One could possibly design a DOM-like
layer in between XSLT and XML if so desired to model XSLT transformations.  My
fundamental logic is that although XSLT may not be "complete" solution, it
doesn't violate the critical orthogonality of design layers (CSS and content
markup, or DOM and content markup).  And I think it does accomplish the main
goal of abstracting (make orthogonal and separate) extensible semantic content
markup from it implementation layer.

I am aware that instead of CSS, XBL can also bind using DOM extensions, but
again this violates the orthogonality between DOM and abstract content markup.

Most of the other benefits of XBL (and XUL) can be accomplished with existing
W3C standards and proposals.  For example, the abstraction of events using
XEvents and the abstraction of procedural code using XForms.

And to build entirely new widgets (as opposed to extending existing ones) not
in XForms or XUL, there is the DOM Views and Formatting proposal I am working
on, to abstract the presentation state.  I'd really appreciate if some others
would enjoin to investigate the importance of this proposal.

http://www.w3.org/TR/DOM-Level-3-Views/views-formatting.html 

(My) Proposal for Improved/Simplified ViewsAndFormatting Segment *abstract*
model
http://lists.w3.org/Archives/Public/www-dom/2002OctDec/0185.html

Exposing the critical ACTUAL style values?
http://lists.w3.org/Archives/Public/www-dom/2002OctDec/0154.html


The original goal of putting behavior in CSS was apparently to provide a way to
"attach style to structured documents":

http://lists.w3.org/Archives/Public/www-style/2001Aug/0029.html

I think this goal can be accomplished without violating the orthogonality
(separation) between markup and style, perhaps similar to how XSL and XSLT are
to be used together to style documents (something I admittedly haven't studied
fully).  Maybe that is already the solution.

In other words, it is not necessary to involve CSS in content markup
abstraction in order to achieve styling exchangability.  CSS sits is an
orthogonal, modular layer separate and independent from content markup (even if
many authors don't use it that way).  See Tim Berners-Lee's "Modular Design":

http://www.w3.org/DesignIssues/Principles#Modular

For example, I have proposed using CSS selector logic to style XEvents. 
Something like this would maintain orthogonality and not cause
interdependencies between the abstract semantics of content markup and the
binding (implementation) of event handlers, i.e. the crucial distinction being
my proposal is abstracting styling of behavior details not semantic *markup* of
behavior:

http://lists.w3.org/Archives/Public/www-style/2002Dec/0077.html

It is very important that we design the W3C standards such that we maintain the
desired abstractness and orthogonality (modularness) of each layer standard. 
For example, the primary goal of content markup is to declare abstract semantic
structure, so that it can be used in powerful ways.  For examples of "ways",
please read Tim Berners-Lee's "principle of least power":

http://www.w3.org/DesignIssues/Principles#PLP

So we don't want standards such as XBL which instead of using existing
standards as "black boxes", instead requires changes to those standards (e.g.
proposed -moz-binding in CSS) which are quite different from the original
abstraction of the standard.

And it is very important that we do not develop redundant standards, per an
essay "What is Good Design?" from Bert Bos, the CSS Chairman:

http://www.w3.org/People/Bos/DesignGuide/redundancy.html

Lastly, using XUL and XBL will undermine use of XSLT and the other redundant
W3C standards mentioned above.

I am assume there will be (hopefully civil and not inflammed :) responses
explaining the things that XBL can do, which W3C standards mentioned above can
not do in unison.  I am interested in these insights, but will also be
considering Tim Berners-Lee's "principle of least power" and the primary goals:

http://www.w3.org/DesignIssues/Principles#PLP


-Shelby Moore
Received on Sunday, 22 December 2002 18:03:46 GMT

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