Well, you have get_class_vars() which can retrieve all the default properties (i.e. the ones declared with 'var $foo').

And your last suggestions is against the nature of PHP. You just do not have to declare variables to use it.

Making this a doc problem though I'm not quite sure; letting the doc team decide.

Yeah, I guess I asked for it. But then I'd have to argue that the var declaration itself is against the nature of PHP! Firstly because it's a declaration, and secondly because it's useless.

Anyway, I understand that there will be major changes in OOP in ZendEngine2, so this is probably not relevant anymore. BTW, when is this ZE2 scheduled to launch? Will it be already in 4.2.0 which is now in RC stage?

So is it (and will it continue to be) valid to use/create class variables not explicitly declared with var?

Currently the following produce the excact same results except that the varaible 'a' will not be returned by get_class_vars.

class foo
{
   var $a;
   function foo()
   {
      $this->a = "test";
   }
};

class foo2
{
   function foo2()
   {
      $this->a = "test";
   }
};

<?
  /**
   * A bugg in php?
   */

   class One {
	   var $a;
	   var $b;

	   /** Print $a & $b */
	   function printVars() {
		    echo("Vareabels: <BR>\n");
			echo("\$a: " . $this->$a . "<BR>\n");
			echo("\$b: " . $this->$b . "<BR>\n");
	   }
   }

   class Two extends One {
		function Two() {
			$this->$a = "A";
			$this->$b = "B";
			$this->printVars();
		}
   }

   $two = new Two;

   echo("<BR>\n");

   print_r(get_object_vars($two));
?>

This code gave the result:

Vareabels:
$a: B
$b: B

Array ( [a] => [b] => [] => B )

Should to work this way?

$this->$a = "A"; // ????

didn't you mean to write 

$this->a = "A";

mind the extra $ in your code, this lead
to "variable variable" expansion, and as
$a was undefined (empty) assingt to 
a member variable named ""

so yes, it should work this way!

Documentations are clear on that.