http://rynite.morris.umn.edu/~elenam/4657_spring07/php/objects/test_point.php 
<?php
  // class names are case-insensitive
class Point {
  private $x;
  private $y;
  static $grid_size = 100;

  function __construct($x = 0, $y = 0) {
    if ($this->check_coords($x, $y)) {
      print "blah\n";
      $this ->x = $x;
      $this ->y = $y;
    }
  }

  private function check_coords($x, $y) {
    if ($x < 0 || $y < 0 || $x > Point::$grid_size || $y > Point::$grid_size)
      return false;
    return true;
  }

  function printp() {
    print "\$x = $this->x \$y = $this->y<br />\n";
  }

  function move($dx, $dy) {
    if ($this -> check_coords($this ->x + $dx, $this ->y + $dy)) {
      $this ->x += $dx;
      $this ->y += $dy;
    }
  }
}

?>

<?php
require_once("point.php");

class ColorPoint extends Point {
  private $color;

  function __construct($x, $y, $color) {
    parent::__construct($x,$y);
    $this -> color = $color;
  }

  function setColor($color) {
    $this -> color = $color;
  }

  function printp() {
    parent::printp();
    print "{$this -> color} <br />\n";
  }
}
?>

<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>
Testing a point class
</title>
<body>
<h2>Testing a point class</h2>
<p>
<?php
require_once("point.php");
require_once("colorpoint.php");

$point1 = new Point(1,3);
print "point1: ";
$point1->printp();

$point2 = new Point();
print "point2: ";
$point2->printp();

$point2->move(5, 7);
print "point2 after the move: ";
$point2->printp();

$color_point = new ColorPoint(3, 7, "red");
print "color point: ";
$color_point->printp();
?>
</p>
</body>
</html>