The Extended version contains exercises for each key for every UST combination over the IIm7 V7 progression in all inversions.
For the jazz piano player, chord voicings is an essential skill, not only for comping (accompanying or laying the chord progression for other players to improvise in) but also to use those voicings as an improvisational aid. All piano players get many melodic ideas or lines from their voicings. There are many ways of practicing and developing a Jazz voicing language. We all know how massive the amount of available combinations is, it seems almost infinite.
A standard approach in creating, learning and/or developing voicings is stacking simple voicings/structures on top of other simple ones. In this manner a richer and more complex sound is created. These structures/chords/voicings are usually called Upper Structures