docs: function(amount) {
        for (var sI = 0; sI < this.slices.length; sI++) {
          var slice = this.slices[sI];
          slice.start = (slice.start + amount);
          // Shift all nested subSlices recursively.
          var shiftSubSlices = function(subSlices) {
            if (subSlices === undefined || subSlices.length === 0)
              return;
            for (var sJ = 0; sJ < subSlices.length; sJ++) {
              subSlices[sJ].start += amount;
              shiftSubSlices(subSlices[sJ].subSlices);
            }
          };
          shiftSubSlices(slice.subSlices);
        }
      }