Messages sent to signals on coupling

I just found out that the track occupation management of the game must have improved at some point in the past, without leaving any trace in any documentation.

On game start-up, “initialise to blocked” is sent once per consist, which means that a signal protecting 3 groups of wagons gets 3 messages.

When you couple up wagons, all the signals which protected that group and the train coupling to it first get an "occupation decrement" message from the system, faking their exit from the block. Then, all the signals protecting the joint train get an "occupation increment" message, faking their entry into the block from the far side.

Track links currently under one of the involved vehicles get the message with parameter "DoNotForward", which means that this message is just for that link, in contrast to the normal messages which need to be forwarded on remote links (numbered 1 and bigger).

These things put together mean that occupation management by the default scripts is far better than it seems by looking at scripts and documentation. Not only is the system aware of multiple groups of wagons on the same track initially, it also does the right thing in the advent of coupling and uncoupling by magically increasing and decreasing the consist count correctly.

The fact that also driverless consists send the "prepare for train" message is a little let-down as I see it currently, because it results in even more unnecessarily cleared signals.