docs: def accession(auth, label, project=None):
      '''
      Get the Accession ID for any Experiment label.
  
      Example:
          >>> import yaxil
          >>> auth = yaxil.XnatAuth(url='...', username='...', password='...')
          >>> yaxil.accession(auth, 'AB1234C')
          u'XNAT_E00001'
  
      :param auth: XNAT authentication
      :type auth: :mod:`yaxil.XnatAuth`
      :param label: XNAT Experiment label
      :type label: str
      :param project: XNAT Experiment Project
      :type project: str
      :returns: Accession ID
      :rtype: str
      '''
      return list(experiments(auth, label, project))[0].id