A. There's no reason it cannot be both.
B. You made an absolute statement without a qualification. I'm beginning to see that is a common thread in some of your posts.
In law: What's black or white (i.e. absolute) is usually very obvious, established, specific, and restricted. The rest is grey, often making it situation specific or principle based. This is both a strength (in that it allows flexibility and a degree of ability to cope with novel situations) and a weakness (in that it often causes laypeople to establish confirmation bias from one positive outcome, or that it can be difficult for people to apply those principles to a non-straight forward instance). Here is a situation where the method to serve a subpoena can almost assuredly be applied to serving any other document upon the Police.