1.php:

/*
class dirMenu {
  var $a1;
  var $a2;
  var $a3;
  var $a4;
  function dirMenu($x1="text1",$x2="text2",$x3="text3",$x4="text4") {
    $this->a1 = $x1;
    $this->a2 = $x2;
    $this->a3 = $x3;
    $this->a4 = $x5;
  }
}
*/

2.php:

$myvar = new dirMenu("xxx","yyy","zzz","qqq");

3.php:

include("1.php");
include("2.php");

--------------------

Trying to execute 3.php you get an error:
Unterminated comment in 1.php
Seems like comments do not really comment class definitions containing errors (like dirMenu where I try to set a4 to $x5 which is not an actual parameter of the function, while I don't understand why it is so critical, really).

Maybe this example won't work (I modified something to make it more common), contact me then, I'll make another one.