def trim_left(self, length, start=0, end=sys.maxint):
        """
        Trim `length` characters off the beginning of each item, in-place,
        from index `start` to `end`.  No whitespace-checking is done on the
        trimmed text.  Does not affect slice parent.
        """
        self.data[start:end] = [line[length:]
                                for line in self.data[start:end]]