code: def _traverse(summary, function, *args):
      
      function(summary, *args)
      for row in summary:
          function(row, *args)
          for item in row:
              function(item, *args)
docs: Traverse all objects of a summary and call function with each as a
      parameter.
  
      Using this function, the following objects will be traversed:
      - the summary
      - each row
      - each item of a row