docs: def rollback(*args, **kwargs):
      '''
      Restore previous revision of Conda environment according to most recent
      action in :attr:`MICRODROP_CONDA_ACTIONS`.
  
      .. versionchanged:: 0.18
          Add support for action revision files compressed using ``bz2``.
  
      .. versionchanged:: 0.24
          Remove channels argument.  Use Conda channels as configured in Conda
          environment.
  
          Note that channels can still be explicitly set through :data:`*args`.
  
      Parameters
      ----------
      *args
          Extra arguments to pass to Conda ``install`` roll-back command.
  
      Returns
      -------
      int, dict
          Revision after roll back and Conda installation log object (from JSON
          Conda install output).
  
      See also
      --------
  
      `wheeler-microfluidics/microdrop#200 <https://github.com/wheeler-microfluidics/microdrop/issues/200>`
      '''
      action_files = MICRODROP_CONDA_ACTIONS.files()
      if not action_files:
          # No action files, return current revision.
          logger.debug('No rollback actions have been recorded.')
          revisions_js = ch.conda_exec('list', '--revisions', '--json',
                                       verbose=False)
          revisions = json.loads(revisions_js)
          return revisions[-1]['rev']
      # Get file associated with most recent action.
      cre_rev = re.compile(r'rev(?P<rev>\d+)')
      action_file = sorted([(int(cre_rev.match(file_i.namebase).group('rev')),
                             file_i) for file_i in
                            action_files if cre_rev.match(file_i.namebase)],
                           reverse=True)[0]
      # Do rollback (i.e., install state of previous revision).
      if action_file.ext.lower() == '.bz2':
          # Assume file is compressed using bz2.
          with bz2.BZ2File(action_file, mode='r') as input_:
              action = json.load(input_)
      else:
          # Assume it is raw JSON.
          with action_file.open('r') as input_:
              action = json.load(input_)
      rollback_revision = action['revisions'][-2]
      conda_args = (['install', '--json'] + list(args) +
                    ['--revision', str(rollback_revision)])
      install_log_js = ch.conda_exec(*conda_args, verbose=False)
      install_log = json.loads(install_log_js.split('\x00')[-1])
      logger.debug('Rolled back to revision %s', rollback_revision)
      return rollback_revision, install_log