Document Si track extension - second batch
Continue the work started in !37303 (merged).
This time, we document the forward extension!
As before, the purpose of the MR is to improve the readability and offer some inline documentation of what is being done for new people looking at the code. No changes to the performance should occur, and I make no attempts to change the elegant existing logic.
Edited by Maximilian Emanuel Goblirsch-Kolb