With a Selector, you can use events to trigger actions.

Events van be :

All kind of Midi message can be used as an Event, using a processor (Hardware tab, section In / Processor).
Midi messages can come also from computer keyboard or joystick
A minima-maxima of a Midi-controller (coming from Midi, mouse, joystick) can also generate en Event with a processor, etc...

The action is linked to the position of the Selector. Example :

Five criteria can trigger a Selector :

If there are more than one chord in the Selector, the "OR" function is applied between the chords

List of Selectors can be displayed, using Help/Shortcuts menu

In case of concurrency between Selectors ( one key appears in more than one Selector ), priority is applied in this order :

Note : "Program" can be used in the Selector as a "caps-lock". Program does not trigger a Selector, but can select between similar Selectors.
Example : to select between two Sequences played with the same key, add Program#1 in the Selector of the Sequence#1, and add Program#2 in the Selector of the Sequence#2. By default, Program#1 is active, so Sequence#1 is played. Selecting Program#2 ( with a keyboard shortcut or a Processor ), Sequence#2 is played. Etc...
With this method, it is possible to have 16 "groups" ( 16 MIDI channels ), with 255 choices each.