The OPmac manual explains how to set the font size and discusses the style variations
\em etc. but I do not see a way to set the actual font in use. I'm using XeTeX and would like to access system fonts. If I set the font using, e.g.
\font\0="Roboto Condensed" at 10pt\0 then the ensuing OPmac style variations give me variations on the default font, so it doesn't seem to be savvy to the change I've made. Is there a "trick" here I can use to inform OPmac of my changed font?
More generally, if there is a package for plain XeTeX that helps with managing font switches like this I'd like to know about it; my searches have come up mostly with packages that manage switching between fonts in the TeX installation.