Each new revision gets a version number that is unique for that file. The number consists of a major and a minor number, separated by a dot. The first revision of a file gets number 1.0. Each newly edited file gets a number that consists of the current major number and a minor number that is higher than any existing one. Typically, revision numbers are handed out in the order 1.0, 1.1, 1.2...
In itself, the numbering scheme of minor numbers is not too interesting, but for two things. First of all, the new minor number is not necessarily one higher than the minor number of the [current] revision. In particular this is not the case when the [current] revision is an earlier one that has been made current. And secondly, all minor numbers within a certain major number are unique.