Became aware of this after reading Termination Shock by Neal Stephenson! Great book. There's a small subplot involving the Line of Actual control (LAC), which is what made me first aware of these rules.
China is slowly flanking India by quietly annexing strategic territory: https://foreignpolicy.com/2021/05/07/china-bhutan-border-vil...
https://www.youtube.com/watch?v=dQJEiGiGc1I