Is mount point index optional?

[promoxer]

From the docs https://pve.proxmox.com/pve-docs/pct.1.html, I interpret that the index after mp is optional, but it does not seem to be so.

--mp[n] [volume=]<volume> ,mp=<Path> [,acl=<1|0>] [,backup=<1|0>] [,mountoptions=<opt[;opt...]>] [,quota=<1|0>] [,replicate=<1|0>] [,ro=<1|0>] [,shared=<1|0>] [,size=<DiskSize>]

I get Option mp is ambiguous when I use --mp ...

I have some scripts that add mount points based on the LXC's needs, would be great if there was an option to just add instead of having to know which index it should be.