Reasonable-seeming entries in /etc/export don't work—why?

I'm trying to learn more about NFS, and I'm experimenting by exporting arbitrary volumes on my M1 Air (running Ventura 13.1) and then mounting them. Often, I write a row to my /etc/exports file and then find that nfsd doesn't do what I expect; I believe it's erroring, though I haven't been able to find any error logs. I've carefully read through man 5 exports but even so, what works and what doesn't seems totally arbitrary to me. In all of my experiments, I add a single row to /etc/exports and then run sudo nfsd restart; sleep 3; showmount -e. I've pasted a table of my results so far below. Does anyone know why nfsd is failing to come up, or showmount -e doesn't show any mounts in the indicated cases below? | /etc/exports entry | Result | | --- | --- | | /Users -network=127.0.0.1 -mask=255.0.0.0 | Works | | /Users -network=127.0.0.0 -mask=255.0.0.0 | nfsd won’t start | | /Users -network=127.0.0.1/8 | showmount -e returns nothing | | /Users -mapall=root -network=127.0.0.1 -mask=255.0.0.0 | Works | | /Users -mapall=root:root -network=127.0.0.1 -mask=255.0.0.0 | showmount -e returns nothing | | /Users/m -network=127.0.0.1 -mask=255.0.0.0 | Works | | /Users/m/test -network=127.0.0.1 -mask=255.0.0.0 | Works | | /Users/m/Documents -network=127.0.0.1 -mask=255.0.0.0 | showmount -e returns nothing | N.B. In the cases where I've written "showmount -e returns nothing", the specific output is this:

$ showmount -e
Exports list on localhost:

$

Where I've written "nfsd won't start", the output is:

$ showmount -e
showmount: Cannot retrieve info from host: localhost: RPC: Program not registered

Removing the line and then running sudo nfsd restart seems to fix it in these cases.