\ifx\luatexversion\thisisundefined \else \directlua local utf8_char, byte, gsub = unicode.utf8.char, string.byte, string.gsub

local function convert_char (char) return utf8_char(byte(char)) end

local function convert_line (line) return gsub(line, ".", convert_char) end

callback.register("process_input_buffer", convert_line)

\fi

† ‡ § ¶