PTR launch parameter?

I’m trying to find out what the PTR’s game code is when launching a game via Battle.net.exe using the --exec=“Launch W3” parameter.

There are code lists for all blizzard (including PTRs) and non blizzard games but haven’t found any for W3 PTR. I tried many variations on W3PTR, W3_PTR, W3T (from uid listed in the PTR shortcut) etc. including different capital and non capital letters combinations, as it is case sensitive, but haven’t found the answer yet.

Does it even exist?