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in luatex-basics-gen.lua
the remapper maps lua to "tex":
local remapper = {
otf = "opentype fonts",
ttf = "truetype fonts",
ttc = "truetype fonts",
cid = "cid maps",
cidmap = "cid maps",
-- fea = "font feature files", -- no longer supported
pfb = "type1 fonts", -- needed for vector loading
afm = "afm",
enc = "enc files",
lua = "tex", --<<<<<<