An example implementation of Key Value Observing in PHP5.3+

kvo.php

<?php

class ExampleClass {

	private $bindings = array();
	
	public function __set($a, $b) {
		$this->$a = $b;
		if(is_array($this->bindings[$a])) {
			foreach($this->bindings[$a] as $bind) {
				$bind['f']($bind['p']);
			}
		}
	}
	
	public function __get($a) {
		return $this->$a;
	}
	
	public function bind($a, $f, $p=null) {
		$this->bindings[$a][] = array(
				'f' => $f,
				'p' => $p
			);
	}
	
}
?>