I am not sure what you mean here. I didn't mean to imply that WOM was special.

Looking at QuarterEnd as another example:

```python
    @property
    def rule_code(self):
        suffix = '-%s' % _month_dict[self.startingMonth]
        return 'Q' + suffix
```

I would not want the Q string both here and in the map,

As for rule_code, I think that it should uniquely identify an offset. To make life simple, I would say the prefix should identify the class and the suffix should identify the arguments for the class.