I try the example, but the 'Range' and 'Comparative' show error: Unknown precedence group. So I add it: precedencegroup Range { } precedencegroup Comparative { } Now, ' lowerThan: Additive ' show error: Precedence group cannot be given lower precedence than group in same module; make the other precedence group higher than this one instead. So,I try make 'Range' or 'Comparative' higherThan any precedencegroup I know, both too. And then, I try change 'Range' to 'RangeFormationPrecedence', 'Comparative' to 'ComparisonPrecedence', it's error too. But this is no error: precedencegroup TestPrecedence {     higherThan: ComparisonPrecedence     lowerThan: RangeFormationPrecedence } I tried everything I could think of, I cann't make a precedencegroup lowerThan custom precedencegroup.