There is a name clash between l3io and l3messages. l3io defines a \iow_newline: (with colon), whereas l3messages requires a \iow_newline (without colon). I am not sure if it should be a function or a variable. * If it is meant to be a variable as documented, \g_iow_newline would be a better name. * Since \err_newline: is a function, \iow_newline: should be a function, too. Ciao Andreas