a. $obj.method ($x + $y) + $z  # means $obj.method(($x + $y) + $z)
b. $obj.method($x + $y) + $z   # means $obj.method($x + $y) + $z
c. $obj.method + 1             # means ( $obj.method ) + 1
d. $obj.method +1              # means $obj.method( 1 )
e. $obj.method+1               # an error!