I've been doing a bunch of reading about objects and overloading in
PHP5, but I've got a couple of questions that I can't seem to find the
answer to online. Suppose the following code in PHP5.2.4:

<?php
class foo {
public $x;
private $z = 'z';

public function __set ($name, $val) {
echo "Setting \$this->$name to $val...\n";
$this->{$name} = $val;
}

public function __get ($name) {
return "The value of $name is {$this->{$name}}.\n";
}
}
?>

My questions are as follows:

1) It seems that the getter and setter are not called on every single
call. For example, if I do the following:

$bar = new foo;
$bar->x = 'x';

There is no output. I would expect to see "Setting $this->x to x."
Another example:

$bar = new foo;
$bar->y = 'y';
echo $bar->y;

I would expect this to see "The value of y is y." but instead I just
get 'y' as output. So when do the various setters/getters get used?

2) It seems that getters ignore the visibility of properties. Why is
this? For example:

$bar = new foo;
echo $bar->z;

I would expect this to throw an error about accessing a private
member, but it outputs "The value of z is z." just fine. If I remove
the __get() overloader, an error is thrown.

I'm guessing that the answer to all of my questions is some how
wrapped up in visibility and overloading. Unfortunately I cannot find
any resource that documents the interactions. TIA.