docs: def addLeadingToGroups(self, proteinIds, groupIds):
          """Add one or multiple leading proteins to one or multiple protein
          groups.
  
          :param proteinIds: a proteinId or a list of proteinIds, a proteinId
              must be a string.
          :param groupIds: a groupId or a list of groupIds, a groupId
              must be a string.
          """
          for groupId in AUX.toList(groupIds):
              self.groups[groupId].addLeadingProteins(proteinIds)
              self._addProteinIdsToGroupMapping(proteinIds, groupId)