@option{--file=@-collection.tar} is considered to be @emph{one} argument.
If you substituted any other string of characters for
@kbd{collection.tar}, then that string would become the name of the
@option{--file=@-collection.tar} is considered to be @emph{one} argument.
If you substituted any other string of characters for
@kbd{collection.tar}, then that string would become the name of the