docs: def update(self, d):
  		"""
  		From a dictionary of offsets, apply each offset to the
  		corresponding segmentlist.  NOTE:  it is acceptable for the
  		offset dictionary to contain entries for which there is no
  		matching segmentlist; no error will be raised, but the
  		offset will be ignored.  This simplifies the case of
  		updating several segmentlistdict objects from a common
  		offset dictionary, when one or more of the segmentlistdicts
  		contains only a subset of the keys.
  		"""
  		for key, value in d.iteritems():
  			if key in self:
  				self[key] = value