Re: <insert> and external entity references

lilley (lilley@afs.mcc.ac.uk)
Wed, 20 Mar 1996 11:48:37 +0000 (GMT)


From: lilley <lilley@afs.mcc.ac.uk>
Message-Id: <22763.9603201148@afs.mcc.ac.uk>
Subject: Re: <insert> and external entity references
To: bsittler@mailhost.nmt.edu (Benjamin C. W. Sittler)
Date: Wed, 20 Mar 1996 11:48:37 +0000 (GMT)
Cc: www-html@w3.org
In-Reply-To: <Pine.SUN.3.91.960319182146.17322A-100000@gray> from "Benjamin C. W. Sittler" at Mar 19, 96 06:23:07 pm

 Benjamin C. W. Sittler writes:
 
> On Wed, 20 Mar 1996, Abigail wrote:

> > Murray Altheim wrote:
> > ++ This would really be the big change: not using HTML as the base language of
> > ++ the Web. We'd use SGML (MIME type "text/sgml; level=1|2|3|4"), allowing the
> > ++ DOCTYPE of the document to determine the DTD, just as in SGML. 

> > If each document comes with its own DTD, then what? A user agent
> > knows how to parse it, but how should it be displayed? Of course,
> > authors could be required to deliver a style sheet as well, but
> > they have to include everything, as there cannot be user agent
> > defaults to fall back on.

This has been reported as a problem with SGML authoring tools.  I recall
someone saying that Author/Editor would not edit a (valid) HTML 3
document because the tables part of the DTD was not implemented in the
way that software expected.  (I tried to find the reference, but it was
not in my own folders and the archives are being slow at the moment.)

I agree that it could be difficult to implement an arbitrary new
element.  Suppose for example that the A and IMG tags did not exist.
Describing the functionality using just a DTD is not possible - OK so
there is this href attribute but what do you do with the string?

> A style and semantics language like dsssl could solve this, at least for 
> a known DTD. Each DTD can refer to a dsssl program which renders it.

I would love to see something like this demonstrated.  Are any of the
SGML companies going to be demonstrating a browser built on DSSSL at the
Paris WWW5 conference?

If so, an implementation of the embed/inset/object/whatever element
using just a DTD and a DSSSL stylesheet[1] would be most interesting.

> > And what about user preferences? How
> > is a user supposed to set preferences, if each document can have
> > unknown elements?

CSS1 solves this with the cascade, so that user preferences and author 
preferences both influence the final presentation. I am not sure how DSSSL 
achieves this, but I expect it can - anyone care to describe the process?

Another thing with unknown elements is that they can inherit properties from 
their enclosing elements. So if for example you have

<body>
  <foo>stuff</foo>
</body>

and body is set in the user preferences to have one inch margins and be in 
14 point dark grey Optima, foo will inherit these properties unless the author 
provided a different rendering.

[1] DSSL can describe more that just stylesheets so what is the correct 
term? A DSSL document? DSSSL program?

-- 
Chris Lilley, Technical Author and JISC representative to W3C 
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