Bug 477787

SUMMARY
Some most popular tablets have the ability to switch modes of the touch ring or the touch strip. Bassed on the mode the shortcut assigned to the touch ring changes so that use can choose which shortcut to use depending on the situation. For example in mode 1 user can have zoom in and zoom out shortcuts mapped to the touch ring and in mode 2 they can have shortcut to resize the brush. 

This helps the artists to quickly utilise multiple shortcuts in the same touch ring without the need to take away the hand from the tablet.

Libinput too supports this. here is the documentation for it - https://wayland.freedesktop.org/libinput/doc/latest/tablet-support.html#tablet-pad-modes

If you want to read more here is the description page of the touch ring on wacom website. - https://101.wacom.com/UserHelp/en/TouchRing.htm notice there is a diagram showing 4 different modes shown by a led indicator besides the touch ring.