docs: def to(items, output=None):
      """Present a collection of items as TSV
  
      The items in the collection can themselves be any iterable collection.
      (Single field structures should be represented as one tuples.)
  
      With no output parameter, a generator of strings is returned. If an output
      parameter is passed, it should be a file-like object. Output is always
      newline separated.
      """
      strings = (format_collection(item) for item in items)
      if output is None:
          return strings
      else:
          for s in strings:
              output.write(s + '\n')