This page allows you to change the key modifiers for any of the available buttons of your input devices (mouse, stylus, etc.), except for the primary button. This can be used to change the actions performed on the canvas when a certain button in combination with a key modifier is pressed.
Modifiers
Clicking on this button with one of the buttons of your input devices (except the primary button) allows you to change the command that each modifier for that button performs when used.
When clicked, it shows a list of the current commands assigned to each of the modifiers for the button you clicked. Only the modifiers that have commands attached to them will be shown. You can add a new item to the list by clicking the button below the list, or remove a modifier that you don't need by clicking the button to the right of each item.
To change what a modifier does, click on the list, which will show you all available choices. To change the modifier that performs a command click on the modifier column on the left and press the modifier or modifiers that you would like to use. Multiple modifiers are allowed, e.g. Shift+Ctrl+middle mouse button (shown as button 2 of System Aggregated Pointer), is by default attached to Rotate View by 15 degree steps.
Clicking this button resets all modifiers for your input devices to their default values.