Answer 1

Like in many other languages the % operator is known as modulo operator, it returns the remainder from division of left-hand operand by right-hand operand. There is this difference output in some language when the right-hand operand is greater than the left-hand one, but mostly, in such case, the operator returns the left-hand operand.

Examples:
echo (7 % 3);
// 7 / 3 = 2
// Remainder 1
echo (10 % 2);
// 10 / 2 = 5
// Remainder zero
echo (0 % 3);
// Zero can't be divided by 3.
// Yields left-hand operand (zero)

Hth, cmiiw