def backward(self, j=<NUM_LIT:1>):
if j < <NUM_LIT:0>:<EOL><INDENT>return self.forward(-j)<EOL><DEDENT>assert self.__i - j >= <NUM_LIT:0>, '<STR_LIT>' % self.__i<EOL>self.__i -= j<EOL>return self[self.__i:self.__i+j]<EOL>
Move backward by j steps.

        >>> b = Buffer('abcdef')
        >>> b.backward(-3)
        'abc'
        >>> b.backward(2)
        'bc'