old_contents: 
  class Instrument(object):
      """Manage and analyze data from multiple pysat Instruments.
  
      FIXME document this.
      """
      def __init__(self, instruments = None, name = None):
          if instruments and name:
              raise ValueError('When creating a constellation, please specify a '
                               'list of instruments or a name, not both.')
          elif instruments and not hasattr(instruments, '__getitem__'):
              raise ValueError('Constellation: Instruments must be list-like.')
          elif not (name or instruments):
              raise ValueError('Constellation: Cannot create empty constellation.')
  
          # FIXME
          pass
      
  
new_contents: 
  class Constellation(object):
      """Manage and analyze data from multiple pysat Instruments.
  
      FIXME document this.
      """
      def __init__(self, instruments = None, name = None):
          if instruments and name:
              raise ValueError('When creating a constellation, please specify a '
                               'list of instruments or a name, not both.')
          elif instruments and not hasattr(instruments, '__getitem__'):
              raise ValueError('Constellation: Instruments must be list-like.')
          elif not (name or instruments):
              raise ValueError('Constellation: Cannot create empty constellation.')
  
          # FIXME
          pass
      
  
subject: Fix typo.