When and how to use add-on control keyswitches in expression maps

I have an external vst that offers additional features like vibrato and attack via keyswitch if required. When I specify say fast attack as an add-on control Dorico creates a totally new keyswitch line for it in an expression map but it’s also possible to specify fast attack as an additional keyswitch line for an individual articulation. I’m confused as to which option I should use. Vibrato is another example. It seems it can be specified as an additional keyswitch line for an articulation or specified totally separately as an add-on control in its own right. I need some clarification on the function of add-on controls.

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An add-on switch is used simultaneously with any base switch. But the base switch only works one at a time. In other words, an add-on switch is a temporary switch that modifies the base switch in some way. I use an add-on switch for con sordino strings because it’s coded instead of recorded in my library and it can be applied to any articulation. This means for me a difference between setting up a single add-on switch versus making a copy of every single base switch and then adding that additional parameter to each one manually to make it a con sordino.
Understanding how articulations are programmed in the library is critical to determine how effective using add-ons can be. But speaking generally, an add-on switch can theoretically be used for any articulation that works by using a temporary additional parameter relative to some basic state: for instance, vibrato, molto vibrato, non-vibrato, legato, sul tasto and so on. But it needs very careful consideration and planning to set up.


Thank you @ebrooks for that guidance. As you suggest I will first make sure I understand the external library first, particularly the way attributes like vibrato can be turned on and off so they’re only present when necessary.