code: public void maybeAppendColumn(Cell cell, DeletionInfo.InOrderTester tester, int gcBefore)
      {
          if (cell.getLocalDeletionTime() >= gcBefore && !tester.isDeleted(cell))
          {
              internalAdd(cell);
              sortedSize++;
          }
      }
docs: Adds a cell, assuming that:
  - it's non-gc-able (if a tombstone) or not a tombstone
  - it has a more recent timestamp than any partition/range tombstone shadowing it
  - it sorts *strictly after* the current-last cell in the array.