Why is powershell scripts extenson .ps1?

I am wondering why powershell scripts extension is .ps1 - why is it not just .ps or .pss (for powershellscript). What dos 1 mean?

1 is the version of the language engine. The idea is that, if they ever had to radically change the language, they could switch to .ps2, and earlier versions would know not to try and run those scripts.

That makes sense. Thanks.