There are specific comments already, but multiple successive slashes are treated as a single slash, in every case except when a path begins with exactly two slashes, in which case it's implementation dependent.

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1...

You can use it to configure the build mode: `build/bootstrap/make.com -j8 MODE=rel o/rel/blink/blink`; no MODE will build a default config. This is used across all cosmopolitan projects; for example, this is for redbean: https://redbean.dev/#source.