UACC Key Switch (UACC KS) is a mixture of keyswitching and UACC which provides the advantages of both methods. When UACC KS is activated a single key switch becomes available. Using the UACC spec outlined here the velocity of this key switch is used to switch articulations.
To use UACC KS instead of key switching first you must lock articulations to UACC KS. Using Chamber Strings as an example, first you must open the expert view by clicking the small black spanner icon outlined in red in the image below.
Next you simply click the small padlock (outlined in green) that has now appeared in the sidebar and choose lock to UACC KS from the dropdown menu (outlined in blue), now you will see a single red KS key as shown below:
For example pressing the key switch at a velocity of 70 would switch to the Trill (minor 2nd) articulation while pressing at velocity 56 would switch to Short Pizzicato (again the velocity values are on the specification found here). As with UACC, you can manually input these velocity values but it's easier to use your DAW or tablet app's functionality.
The main advantage of UACC KS over UACC is that you can layer articulations by overlaying the notes of the key switch on the piano roll. This is why we advise using UACC KS when building articulations sets in Logic.