The current version of the standard from June 2006 contains some inconsistencies (e.g. covariant redefinitions). Historically, there were many definitions and redefinitions. Tainan's complex history of comebacks, redefinitions and renewals inspired its popular nickname "the Phoenix City". Many revisions and redefinitions have taken place since then. Subsequent redefinitions of the metre and kilogram mean that this relationship is no longer exact. The redefinitions did not mean that a lot of railways were changed. Such redefinitions however are not universally accepted and are still subject to debate.