Should really appear the play panel in the Dynamics page of the handbook?
I'm not sure if play panel should appear in the handbook page related to dynamics. I think that it's not the same the Volume than dynamics. Volume has to do with loud and soft. Is maybe a parameter wich you can use to adapt the music to the needings of a situation: High volume for a big place with lots of people, a low volume to allow people to speak despite the music... Dynamics has more to do with intensity and expresion. One way to show intensity is to play loud a sound, but there are other things like attack and articulation or sound colour on wich dynamics depend.
Besides, dynamics depend on each other. Forte must "seem" louder than mezzo-forte, but softer than fortissimo. If volume where a box wich contains music with diferent dynamics, I would say that volume doesn't depend on the things that are inside of it. It behaves like a frame for dynamics. With a low Volume, a forte "seems" still forte.
Taking into account that the users of this program are musicians, I must say that I don't speak to my students in terms of volume and my teachers didn't with me.