def scan_prefix(self, prefix, feature_names=None):
        '''Scan for FCs with a given prefix.

        :param str prefix: Identifier prefix.
        :param [str] feature_names:
          A list of feature names to retrieve. When ``None``, all
          features are retrieved. Wildcards are allowed.
        :rtype: Iterable of ``(content_id, FC)``
        '''
        resp = self._scan_prefix(prefix, feature_names=feature_names)
        for hit in resp:
            yield did(hit['_id']), self.fc_from_dict(hit['_source']['fc'])
Scan for FCs with a given prefix.

        :param str prefix: Identifier prefix.
        :param [str] feature_names:
          A list of feature names to retrieve. When ``None``, all
          features are retrieved. Wildcards are allowed.
        :rtype: Iterable of ``(content_id, FC)``