code: def PlaceUOffsetT(self, x):
          
          N.enforce_number(x, N.UOffsetTFlags)
          self.head = self.head - N.UOffsetTFlags.bytewidth
          encode.Write(packer.uoffset, self.Bytes, self.Head(), x)
docs: PlaceUOffsetT prepends a UOffsetT to the Builder, without checking
          for space.