Hi, I have some question about on_error behavior. - Why the error explanation is only shown when the user changes a number by a some other characters?, may be because there is not rule for "+-/*" ? is it necessary to be a rule to show where the error is? - When is useful to write more than one on_error?, may be when you want to show different messages for each different rule? - What is the rule to use as on_error first parameter?, I guess the most general rule of the parsing zone. Thanks & Regards. Xavi.