l3backend: adding new DVI specials?

[Joseph Wright]

On 19/02/2020 10:42, Joseph Wright wrote:
> On 19/02/2020 10:08, Norbert Preining wrote:
>> Hi Joseph,
>>
>>> The problem with saying 'disable the backend' is what then happens with
>>> things that *need* them, such as colour, rotation, hyperlinks, etc. The
>>
>> I understand, but none of them are interpreted, only "color" special is
>> interpreted by pyxplot. It does not contain arbitrary TeX documents,
>> just minimal latex document with a page containing the plot.
> 
> Sure, but starting from the 'writing support macros' end we want to have 
> a known set of functions. At present, I can't even find information on 
> what type of colour specials pyxplot supports.
> 
>>>      \PassOptionsToPackage{backend = dvipdfmx}{expl3}
>>
>> Maybe I do it wrong, but that does not work:
>>     \PassOptionsToPackage{backend = dvipdfmx}{expl3}
>>     \documentclass{article}
>>     \begin{document}
>>     Hello World
>>     \end{document}
>> still contains the dvi special for loading l3backend-dvips.pro
> 
> I realised that after I sent it: you'd need to explicitly load expl3. 
> Probably best just to
> 
>      \RequirePackage[backend=dvipdfmx]{expl3}
> 
> although you could force in various other ways.
> 
> Joseph

We have a better plan to be released probably tomorrow. I'm going to add 
a new option "suppress-backend-headers" which will do exactly what it 
says. Once things are updated

     \ExplSyntaxOn
     \keys_set:nn{sys}{suppress-backend-headers=true}
     \ExplSyntaxOff

will do the job: put that anywhere before \begin{document}, so e.g. 
right at the start of a run.

Joseph