Our local dept uses "Break" when you are (essentially/functionally) splitting a single radio transmission into separate functional components.
ie; "[scene command] acknowledges unit X is onscene BREAK [scene command] to dispatch, please dispatch another unit for ...". First part ack'd a scene transmission, second part was from the scene commander to dispatch, all on the same keydown. It is widely accepted (and at some time confusing) practice that when a transmission ends, that the information therein is considered to be complete. A listener who is multitasking can(and will) 'tune out' to some level when the transmission is not directed to them, and this helps draw attention that this is a compound transmission. Appropriate utilization can help with OTA congestion.
They also use "Check" when they have a slip of the tongue and have to immediately correct a part of a transmission, within that transmission.
ie; "[scene unit] to responding medic, the pt's blood pressure is 170/40 right now, CHECK , 70/40...". Same keydown, correction of information within.