>While the reason may be optional, I firmly believe that the status code itself must be present
I agree with Jacob.
Perhaps
The 451 status code is optional; clients cannot rely upon its use. It is imaginable that certain legal authorities may wish to avoid transparency, and not only forbid access to certain resources, but also disclosure that the restriction exists. should be changed to The 451 status code is mandatory in a compliant implementation. However clients cannot rely upon its use. It is imaginable that certain authorities may wish to avoid transparency, and not only forbid access to certain resources, but also disclosure that the restriction exists.
>- o Description: Unavailable for Legal Reasons >+ o Description: Resource Unavailable, Censored and Redacted Another way of looking at this is ... the current 403 Forbidden status should be clarified as only being used in the scenario that the content owner on the origin server freely chooses not to permit access and 451 should be used in all scenarios when the content owner on the origin server would permit access but for external constraints. Hence something along the lines of o Description: Forbidden due to external constraints This would cover a range of scenarios including legal injunction against the content owner, pressure on the content owner that does not have formal legal standing, interference by intermediate devices, ...