code: def forward(self, j=1):
          
          if j < 0:
              return self.backward(-j)
          self.__i += j
          return self[self.__i-j:self.__i]
docs: Move forward by j steps.
  
          >>> b = Buffer('abcdef')
          >>> b.forward(3)
          'abc'
          >>> b.forward(-2)
          'bc'