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Design for (interactively) customizable DSSSL stylesheets

From: "Norbert H. Mikula" <nmikula@edu.uni-klu.ac.at>
Date: Fri, 28 Mar 1997 10:08:52 -0800
We are already at the point where we are able 
to write easy to maintain and modular stylesheets.
(Looks like, after all, what we have learned from software 
engineering has made its way into DSSSL practice. 
Yet another item where it shows how good it is that DSSSL
is *very* close to a programming language).

One of the problems that I am struggeling with right now,
is that I want to design user agents via which you can
customize your stylesheet interactively (I am having
in mind for instance a (my) XML/DSSSL based WWW browser).

How can I tell the user agent what things are customizable.
I can take the whole stylesheet and make it editable 
for the user, but that would scare off most of them.

If we look at a (well-done) stylespec there are only a few
variables on which all others depend on. Examples for such
variables could be document-font-size, para-space-before(after) ...
The others are very often derived from these and/or inherited. 

FYI: I think good examples for such styles are the DOCBOOK style,
the TEI style and of course Jon's HTML style.

So my idea would be to take these variables and make them
editable by the user.

But..., how do I know which ones are these variables and
which are really relevant for the user. The
stylesheet designer knows it. Why don't we create a seperate
style module where we put all these variables in.
(We don't need to extend DSSSL for that. We can use what is
already there).

The problem, I guess, wouldn't be solved completely, however.
The user agent would look at lot better if we could
ad some textual information to the variable. 

What I have in mind looks like :

(define-extended "Basic font-size for the document " doc-general-fn-size
12pt) 

This would define the variable to the DSSSL engine and keep
the information that would be given the user agent.

Or, what just came into my mind. We have one module
where we have the "classical defines" and another module
where we do the extedend define :

Module A :

(define fn-size 12pt)

Module B :

(define-extented "Basic font-size for the document " fn-size)

That way we wouldn't have conflicts for tools that don't
want to deal with this extended definitions.

Please let me know what you think about it !

-- 
Best regards,
Norbert H. Mikula

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