def __setitem__(self, key, value, dict_setitem=dict.__setitem__):
            # Setting a new item creates a new link which goes at the end of the linked
            # list, and the inherited dictionary is updated with the new key/value pair.
            if key not in self:
                root = self.__root
                last = root[0]
                last[1] = root[0] = self.__map[key] = [last, root, key]
            dict_setitem(self, key, value)
Adds an option to the AST, either as a non-block option or for an
dataset/ETHPy150Open xraypy/xraylarch/doc/sphinx/ext/backports.py/OrderedDict.__setitem__--crossover with--dataset/ETHPy150Open xtrementl/focus/focus/parser/parser.py/SettingParser.add_option