aboveHighWater example

// Preparing the row gives source plugins the chance to skip.       if ($this->prepareRow($row) === FALSE) {
        continue;
      }

      // Check whether the row needs processing.       // 1. This row has not been imported yet.       // 2. Explicitly set to update.       // 3. The row is newer than the current high-water mark.       // 4. If no such property exists then try by checking the hash of the row.       if (!$row->getIdMap() || $row->needsUpdate() || $this->aboveHighWater($row) || $this->rowChanged($row)) {
        $this->currentRow = $row->freezeSource();
      }

      if ($this->getHighWaterProperty()) {
        $this->saveHighWater($row->getSourceProperty($this->highWaterProperty['name']));
      }
    }
  }

  /** * Position the iterator to the following row. */