def is_set(self, key):
        """Check to see if the key has been set in any of the data locations.
        """
        path = key.split(self._key_delimiter)

        lower_case_key = key.lower()
        val = self._find(lower_case_key)

        if val is None:
            source = self._find(path[0].lower())
            if source is not None and isinstance(source, dict):
                val = self._search_dict(source, path[1::])

        return val is not None
Check to see if the key has been set in any of the data locations.