list operators (rightward)

[Pine Yan]

I saw there two sections in perl reference mention about list operators.

http://perldoc.perl.org/perlop.html

First one is 
Terms and List Operators (Leftward)

and second one is 
List Operators (Rightward)

I don't quite get what it want to tell very well. Looks like the first
one discusses case
with () after a function call, and the second means no () after function
call. Am I right?

I tested both case in script and find out that both works from left to
right:
First:
        $a = 1, $b = 2, $c = 3, $d = 4;
        print (($c = $c+$d), " ", ($b= $b+$c)," ",  ($a = $a+$b), "\n");

and second:
        $a = 1, $b = 2, $c = 3, $d = 4;
        print +($c = $c+$d), " ", ($b= $b+$c)," ",  ($a = $a+$b), "\n";

both get result:
        7 9 10

So what does the leftward/rightward exactly mean here?

Sincerely
Pine