mailutils options confusing

[Alain Magloire]

# messages --help
Usage: messages [OPTION...] [mailbox...] 
GNU messages -- count the number of messages in a mailbox

 Common mailutils options
  -L, --license              print license and exit
  -m, --mail-spool=URL       use specified URL as a mailspool directory

 messages specific switches:
  -q, --quiet                Only display number of messages
  -s, --silent               Same as -q

  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.


Is it possible to rephrase the "Mandatory or optional ..."
I have no idea what it means.