[EXT] Re: l3backend: adding new DVI specials?

Philip Taylor P.Taylor at Rhul.Ac.Uk
Fri Feb 14 13:47:21 CET 2020

Zdeněk Wagner made three different points :


    That a universal special would be equivalent to developing a new language


    That different drivers require different specials to be inserted at different points in the source code


    That a special that cannot be handled by a particular driver should result in a warning.

I will address each in turn.

 1. I do not agree.  The underlying languages remain unchanged — all I
    am proposing is that the \specials become polyglot, and add a tag
    identifying the language in which each component is expressed.
 2. Is easily addressed by including /all/ necessary specials in the
    source document at the appropriate places; a driver would then
    interpret only those elements of each \special that are targetted at
    that particular driver.
 3. Is the crux of the matter, but directly conflicts with David's point
    about regression testing.  Therefore we need to add one further
    \special, at the very beginning of the document, to indicate whether
    or not subsequent \specials should lead to warnings if not
    understood by any particular driver.

But perhaps the last is all that actually need to be implemented — a 
universal \special, understood by all drivers, that indicates whether or 
not a warning should be issued when an unrecognised \special is 
encountered ...  Turn on for regression testing, off for production.

** Phil.
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