docs: def listdir( self, folder_id='0',
  			type_filter=None, offset=None, limit=None, **listdir_kwz ):
  		'''Return a list of objects in the specified folder_id.
  			limit is passed to the API, so might be used as optimization.
  				None means "fetch all items, with several requests, if necessary".
  			type_filter can be set to type (str) or sequence
  				of object types to return, post-api-call processing.'''
  		res = yield super(txBox, self).listdir(
  			folder_id=folder_id, offset=offset,
  			limit=limit if limit is not None else 900, **listdir_kwz )
  		lst = res['entries']
  		if limit is None: # treat it as "no limit", using several requests to fetch all items
  			while res['total_count'] > res['offset'] + res['limit']:
  				offset = res['offset'] + res['limit']
  				res = yield super(txBox, self).listdir(
  					folder_id=folder_id, offset=offset, limit=900, **listdir_kwz )
  				lst.extend(res['entries'])
  		if type_filter:
  			if isinstance(type_filter, types.StringTypes): type_filter = {type_filter}
  			lst = list(obj for obj in lst if obj['type'] in type_filter)
  		defer.returnValue(lst)