According to the rules of syntax.

Of, related to or connected with syntax. / Containing morphemes that are combined in the same order as they would be if they were separate words e.g. greenfinch

syntactic, related to syntax

(relatively rare) syntax

(computing) Additions to the syntax of a computer language that make code easier for humans to read or write, but that do not change the functionality or expressiveness of the language.

(computing) Additions to a computer language that make it harder to write bad code.