In the event that your input device has more than two buttons, there are some additional default button assignments for them:

• If you have three mouse buttons, the middle button is mapped by default to a logical button called "XButton 1." XButton 1 has some additional button assignments. It has assigned to it key-ins that allow you to pan, rotate, or navigate through views, depending on whether you press XButton 1 alone or with the <Ctrl>, <Alt>, or <Shift> key. You can change XButton 1's button assignments to do something other than pan, rotate, or navigation through views, which is why the button has a generic name.
• If you have more than three physical buttons on your input device, note that buttons four through 15 are mapped to logical buttons XButton 2 through XButton 13. You could add a button assignment to your fourth button, for example, which is mapped to logical button XButton 2. In the Button Assignments dialog you would assign a key-in to XButton 2. You also could add the <Ctrl>, <Alt>, and/or <Shift> keys to XButton 2. Pressing your fourth button, plus the other keys if you added them, would execute the key-in.