Robuta

https://tug.org/pipermail/xetex/2007-August/007255.html

[XeTeX] defining fonts in plain TeX files

plain tex xetex defining fonts files

https://www.tug.org/pipermail/texhax/2022-December/025901.html

plain TeX: undefined control sequence \protected - texhax mailing list - TeX Users Group

plain tex control sequence mailing list undefined protected