Dear Philip, xdv2pdf was a driver for MacOS by Jonathan. If you use -no-pdf option and apply xdvipdfmx to a created .xdv file, you can see messages like
xdvipdfmx:warning: xetex-style \special{x:rulecolorpush} is
not supported by this driver;
I don't know details, perhaps \special{x:something}
may not be supported in xdvipdfmx except for a few ones.
Best,
Akira
