Indeed both are in-game as long as I remember the Rails themselves. You should've performed tests, or at least watched the video tutorials by
Bench, which provided the necessary information on official release.
Activators and Buttons adjacent to the rail both recieve the signal when entity is docked or finishes the rotation phase in case of rotator rails. IIRC, Button is triggered once, while Activators are triggered on until the entity is undocked.
Linking either Buttons or Activators to the rail block, without any other rails adjacet to them, will decouple the entity from that rail block on activation. If adjacent rail is present near said Button or Activator, it will change all linked rails to the adjacent rail, both by type and direction.