I would imagine it is an implicit rule (rather than explicit) due to site meta and expectations. (Granted, I will say that I wasn’t aware this was a thing til now.)In post 64, Umlaut wrote:I can't find this rule anywhere.In post 62, callforjudgement wrote:Normals already ban duplicates (except in obvious cases like Neighbour).
Also, I do believe that sole already exists in the form of Informed.