Macro __mx_conversion_arg_message 

#[doc(hidden)]
macro_rules! __mx_conversion_arg_message {
    ($e:expr, $name:expr) => { ... };
}

Internal: the whole message of a failed argument conversion whose error words it itself (a match_arg choice error, see ConversionArgMessageBuiltin, or an error with an argument_message, see ConversionArgMessageClassed), for the argument $name; None otherwise. crate::error_value::conversion_condition_value then uses it in place of <prefix>: <reason>. Not public API.