title: Why revision number in version control does not increase by 1 all the time?
body: <p>When I use "svn log", for example, to view the revision history, I find that the revision number does not increase one by one all the time. For example, one revision has revision number "1234" but its next revision has revision number "1256" instead of "1235". What happens between these two revisions? What their revision numbers are not consecutive?</p>
  
  <p>Thanks.</p>