Math: Product (multiplication)
Product (multiplication) of $a and $b. A can be an array and $b a number, in which case each member of $a gets multiplied by $b. If $a is an array and $b is not provided then array_product is used to return a single numeric value. If both $a and $b are arrays, each member of $a is multiplied against the corresponding member in $b compared using index.
First number for calculation
If TRUE, throws an Exception if argument "a" is not specified and no child content or inline argument is found. Usually okay to use a NULL value (as integer zero).
Second number or Iterator/Traversable/Array for calculation