docs: def _all(field, value, document):
      """
      Returns True if the value of document field contains all the values
      specified by ``value``. If supplied value is not an iterable, a
      MalformedQueryException is raised. If the value of the document field
      is not an iterable, False is returned
      """
      try:
          a = set(value)
      except TypeError:
          raise MalformedQueryException("'$all' must accept an iterable")
  
      try:
          b = set(document.get(field, []))
      except TypeError:
          return False
      else:
          return a.intersection(b) == a