Are multiple variable assignments done by value or reference?

Question

$a = $b = 0;

In the above code, are both $a and $b assigned the value of 0, or is $a just refer

Answer 1

Regard this code as:

$a = ($b = 0);

The expression $b = 0 not only assigns 0 to $b, but it yields a result as well. That result is the right part of the assignment, or simply the value that $b got assigned to.

So, $a gets assigned 0 as well.