[XeTeX] Colour specials for XeTeX

[Philip Taylor]

On 08/06/2020 10:28, Zdeněk Wagner wrote:

>
> The request of supporting dvips specials in xdvipdfmx is not very
> fair. PDF is modelled after PostScript but not the same. PostScript is
> a linear language, PDF lacks programming structures but makes use of
> streams, even indirect streams and indirect objects. PostScript has
> one current colours, PDF has two current colours, one for fill,
> another for stroke. PostScript can directly set both the colour and
> the colour model by setgray, setrgbcolor, setcmykcolor or first change
> the model and then set the colour by setcolor the number of parameters
> of which depend on the current colour model, while PDF needs k and K
> for CMYK, rg and RG for RGB, g and G for greyscale. The colour stach
> is neither a feature of PostScript nor PDF, they are implemented in
> the driver. It is more difficult in PDF, it is more likely to destroy
> something, thus I understand that it is not implemented the same way
> as in dvips. Correspondence between PostScript and PDF is not 1:1
> hence the drivers must convert the same TeX specials in a very
> different way to the target language.

I fear that I have explained myself badly.  I am specifically /not/ 
asking that "xdvipdfmx" support "dvips" \specials in a manner 
identical to "dvips".  All I am asking is for information on where 
"xdvipdfmx"s support for (colour) \specials is documented.  It would 
/seem/ that, modulo the differences necessarily imposed by targetting 
Adobe PDF rather than PostScript, "xdvipdfmx" does indeed support the 
same set of colour \specials as "dvips", but is this fact documented 
anywhere, and are the differences (if any) noted ?

** Phil.