code: def add_icons(self, icons):
          
          _vars, _icons = self._vars, self._icons
          for ic in icons:
              try:
                  if not isinstance(ic, IndividualConstraint):
                      ic = IndividualConstraint(*ic)
              except TypeError:
                  raise XmrsError('Invalid ICONS data: {}'.format(repr(ic)))
              left = ic.left
              right = ic.right
              if left not in _icons:
                  _icons[left] = []
              _icons[left].append(ic)
              # the following should also ensure left and right are in _vars
              if 'icrefs' not in _vars[right]:
                  _vars[right]['icrefs'] = []
              _vars[right]['icrefs'].append(ic)
              _vars[left]
docs: Incorporate the individual constraints given by *icons*.