Quick answer: The chord selector box allows you to select chords for substitution from a range of musically sensible chord choices.
Chord Selector Box in Liquid NotesLiquid Notes provides a drop-down chord selector box for direct selection of chords from a list. This list has been pre-populated for you, showing only musically sensible chord choices, following a deep harmonic analysis of your MIDI arrangement when opening a MIDI file.
Here is an example of the drop-down chord selector box:
The sequence of chords shown follows the harmonic context of your arrangement, starting from the top of the list with rather conventional chords towards the bottom of the list with rather unconventional chords to choose from.
By default, Liquid Notes limits the list of available chords for 'safe' musical results. You may change this setting, read more about it in this article - http://re-compose.desk.com/customer/portal/articles/1389115.