Order of execution of Key Commands with stacks

I know that there are no StackPosition property analogous to the DeckPosition (unfortunetely), but what is the order of execution of KeyCommands on stacks?

From what I understand if multiple stacks are selected, they are processed one after the other, is that correct? Are the stacks fully processed before the command is passed to the next stack?

Now, when executing commands on the stack what is the order? From my tests it seems to be from the bottom piece to the top piece, but I can be sure without knowing the internals of VASSAL. Am I correct in thinking the the commands are sent always to the bottom piece first?