"The mouse has three buttons, and the Blit software maintains a convention about what the buttons do." http://doc.cat-v.org/bell_labs/blit/blit.pdf http://doc.

"The mouse has three buttons, and the Blit software maintains a convention about what the buttons do." http://doc.cat-v.org/bell_labs/blit/blit.pdf http://doc.cat-v.org/bell_labs/blit/blit.pdf RISCOS and Arthur (Acorn Computers, UK) had a three button mouse and the middle button brought up a local menu for the window under the button. I often wondered where that came from...