':return: a list of lists of word/tag/IOB tuples
:rtype: list(list)
:param fileids: the list of fileids that make up this corpus
:type fileids: None or str or list'

def iob_sents(self, fileids=None, tagset=None):

    self._require(self.WORDS, self.POS, self.CHUNK)
    def get_iob_words(grid):
        return self._get_iob_words(grid, tagset)
    return LazyMap(get_iob_words, self._grids(fileids))
