Hello Ulrike, > l3basics contains \luatex_if_engine:... and \xetex_if_engine:... > > I would find similar \xetex_or_luatex_if_engine: I think you are after '\pdftex_if_engine:', as this deals with the case where the engine is pdfTeX or otherwise. (I personally feel \engine_if_... would be clearer for these, but the rest of the team are as-yet unconvinced.) > It seems to work fine. But I'm a bit unsure about the naming of the > command. Is the prefix \ufcore OK? You can pick any prefix you like at present. We do need some way of logging these: I may make some proposals in the near-ish future. -- Joseph Wright