Re: DSSSL Design Question

[Vivek Agrawala <vivek@xxxxxxxxxxxxxxx>]

James Clark wrote:
>
> Since you can declare your own characterstics, why aren't they sufficient?
> 
> I think it would desirable to allow #f instead of a public identifier in
> declare-characteristic, to mean that this isn't a characteristic that has
> semantics that should be passed to the formatter, but rather it's just being
> used to pass information down.
	I like this idea. It would improve the flexibility of DSSSL.

	Can such characteristics be handled completely by the implementation?
	With the current Jade, user-defined characteristics require
	some modification in the backend(s).


> One solution is what might be called first-class modes:
> 
> (element FOO
>   (let ((x (compute-some-info-about-foo))
>         (y (compute-some-other-info-about-foo))
>     (with-first-class-mode
>       (first-class-mode ; new syntax, note that the values of x and y in
> effect get passed down
>         (element BAR
>            (if x ; NB
>               (make simple-page-sequence)
>               (make scroll)))
>         (element BAZ
>            (literal y)))
>       (process-children))))

This seems like a good idea, but appears to be more restrictive than
having arbitrary (read-only) access to the
not-for-formatter-characteristics.

What are the advantages of "First Class Modes" over the
 "Not For Formatter Characteristics" ??


-- Vivek Agrawala
Siemens Corporate Research, Inc.	email: vivek@xxxxxxxxxxxxxxx

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