how come normal user cannot see nfs shares with df?

the Question: where is this officially documented?

cannot find it in eg.: https://linux.die.net/man/1/df

i have a suspicion that it is related to that the user doesn’t have UNIX level permission for those shares.

user@sles:~> df -h|grep -i foobar
user@sles:~> sudo df -h|grep -i foobar
1.2.3.4:/foobar  110G   40M  110G   1% /root/foobar
1.2.3.4:/foobar2  180G  106G   75G  59% /root/foobar2
user@sles:~>

but this can confuse people that just want to list ALL the mounted shares without root permission.