the answer is: the content of the statute.
The content of the statute refers to the written law that written by legislative body in a certain government (in united states , it would be the congress).
A claim that focus on the content of the statue will question/highlight the functional aspect of the statue.When Owen said that the statute infringe his substantive due process, he's basically saying that the statute is does not serve its function since it limit his fundamental rights to conduct a due process.