I don't know if this is standard or a previous owner had added a feature to my propane system, but I think it is a good idea. There is a device that when there is too much flow, i.e. fuel
line is cut, the ball gets pulled into its seat and blocks the flow. Mine is a brass fitting installed just after the connection to the tank.
Here's one I found that is also a tank level indicator. I don't know anything about this particular product. The difference from what's in my system is I have no fuel indicator and it is just part of the fuel line on mine.