$a = 3; # Set the global variable called a (which is a scalar variable, meaning that it can hold either a number or a string - in this case we are using a string) blah blah...
Is not a "moderate" amount of documentation.
Writing your entire program on one-line is also not a "moderate" amount of documentation.
So somewhere in between the two extremes lay a "moderate" amount of attention to readability and documentation.
My statement is that at that point of moderation - in most professional environments - it *should* be expected that the reader knows the precedence table - and therefore documentary parenthesis are not necessary.