10. The computer system of claim 9 , wherein the user input device comprises a stylus.
10. The computer system of claim 9 , wherein the user input device comprises a stylus. 11. The computer system of claim 10 , wherein the stylus has a first end portion and a second end portion, and wherein the memory stores further processor-executable instructions that, when executed by the processor, cause the processor to: detect whether the first end portion of the stylus or the second end portion of the stylus is being moved across the display device; if the first end portion of the stylus is being moved across the display device, then select the ink annotation mode; and if the second end portion of the stylus is being moved across the display device, then select the eraser annotation mode.