NOTE:When there are no registered visualisation clients, this predicate fails with all arguments, and has no effect.If ViewableName is instantiated, tests whether ViewableName is the name of an existent viewable. If not, ViewableName is successively instantiated to the names of all existent viewables.
[Assuming that at least one visualisation client is registered] Success: viewable_create(my_viewable, [X,Y,Z], array([fixed], any)), viewable(my_viewable). Failure: viewable(non_viewable) Exception raised: viewable(123). [raises error 4].