function.php  simple function example
  php source code
  function sum($x, $y) {
    $z = $x + $y;
    return $z;
  }
  $a = sum(5, 10);
  echo "5 + 10 = " .$a. "
\n";
  echo "7 + 13 = " . sum(7, 13) . "
\n";

  5 + 10 = 15

7 + 13 = 20