code: protected function getTagSortSourceColumn($prefix = null)
      {
          $column = $this->get('tag_srcsorting');
          if (!$column) {
              return null;
          }
  
          if (null !== $prefix) {
              return $prefix . '.' . $column;
          }
  
          return $column;
      }
docs: Retrieve the sorting source column.
  
  @param string $prefix The prefix (e.g. table name) for a return value like "<table>.<column>".
  
  @return string