as i understand you just added new types for the choose-elem-button - the syntax did not change?
As soon as i access the element with elem_value() or elem_type(), the game crashes with "Unknown elem type"button =
name = "button-name",
type = "choose-elem-button",
elem_type = "signal",
I made a new choose-elem-button in a fresh and simple mod and got the same error message, so i hope its not on me.