Heiko Oberdiek a écrit : >> (This uses \@nil.) Putting the second split into a macro to test it against >> \@empty is safe, but one might dislike it as "slow". > > I prefer "safe". > I agree. > An expandable test could be used, e.g.: > \ifx\\##2\\% or something else as \\ Is it "allowed" to use e-TeX commands inside the kernel? If so, \expandafter\ifx\expandafter\\\detokenize{##2}\\% or something else as \\ is the safest test, as I'm sure you know. Anyway, depending on the intended use of \in@, certain resctrictions (such as "no unbalanced \if" or "no # token" or "no \@nil token" are probably acceptable, as long as they are properly documented. Manuel.