code: function diffVersions(callback) {
          var prior = null;
          _.each(versions, function(version) {
            if (!prior) {
              version.diff = [ { value: '[NEW]', added: true } ];
            } else {
              version.diff = apos.diffPages(prior, version);
            }
            prior = version;
          });
          versions.reverse();
          return callback(null);
        }
docs: We must diff on the fly because versions get pruned over time