Earlier quoted context omitted.
What happens if that link performs an action upon a GET request? Edit: Folks, I agree with you all, but I've seen a lot of garbage out there. Just asking the question for the discussion.
Then the action needs to be harmless, because GET is defined as not merely idempotent but also safe. Didn't we already learn this lesson after all the unsafe-GET problems unveiled when prefetching browser accelerators came on the scene in, IIRC, the late 1990s?
I generally see PUT and PATCH classified as idempotent (for the same input).