https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116399
--- Comment #16 from corentinjabot at gmail dot com --- Requiring size or common would force internal representation strategies. With the current set of requirements, you could, for example, store all the names in a giant array or string and #embed it, if you so desired. `common` would preclude that sort of strategy, and size would require additional data to store the size in a way that is still `O(1)`. I don't see use cases for that, and neither did WG21 - I believe it was briefly discussed when we added the random_access/borrowed requirements. (and we don't want to make these tables more annoying for implementers than they have to be :D)
