docs: def modAminoacidsFromLabelInfo(labelDescriptor):
      """Returns a set of all amino acids and termini which can bear a label, as
      described in "labelDescriptor".
  
      :param labelDescriptor: :class:`LabelDescriptor` describes the label setup
          of an experiment
  
      :returns: #TODO: docstring
      """
      modAminoacids = set()
      for labelStateEntry in viewvalues(labelDescriptor.labels):
          for labelPositionEntry in viewkeys(labelStateEntry['aminoAcidLabels']):
              for modAminoacid in aux.toList(labelPositionEntry):
                  if modAminoacid != '':
                      modAminoacids.add(modAminoacid)
      return modAminoacids