Constant REPEATABLE_PARAMETER 

const REPEATABLE_PARAMETER: u64 = 0x03;

The one parameter type whose own definition lets it repeat.

Section 9.2.1.1: “The AUTHORIZATION TOKEN parameter MAY be repeated within a message.” That is the “unless the parameter definition explicitly allows multiple instances” carve-out of Section 9.2, and on this draft it is the only one — the other two version-specific parameters and all five setup parameters say nothing of the kind.

The same code point, 0x03, in both namespaces: Section 9.2.1.1 assigns it to the message parameter and Section 9.3.2.5 defines the setup parameter as “See Section 9.2.1.1”, so a sender may repeat it in a SETUP as well.