Are arrays in PHP copied as value or as reference to new variables, and when passed to functions?

1) When an array is passed as an argument to a method or function, is it passed by reference, or by value? 2) When assigning an array to a variable, is the new variable a reference to the original array, or is it new copy? What about doing this: $a = array(1,2,3); $b = $a; Is `$b` a reference to `$a`?