[NTG-context] Cannot build plain format

Dear list, I'm trying to build the plain format but it fails with $ mtxrun --script plain --make [...] ! I can't find file `luatex-plain.tex'. but mtxrun can find the file. $ mtxrun --find-file "luatex-plain.tex" /opt/context/tex/texmf-context/tex/generic/context/luatex/luatex-plain.tex What am I doing wrong? Also another question: Does LMTX come with a plain format? Cheers, Henri