Alternative to parent::$foo, rather than using that syntax, since accessors shadow properties, we could use $this->foo which would either access the property directly or call the parent foo accessor until there was no parent accessor which $this->foo would then access the property directly.

gistfile1.php

class A {
  public $foo {
		get { return $this->foo ?: 'unknown'; }
		set { $this->foo = $value; }
	}
}

class B extends A {
	public $foo {
		get { return $this->foo ?: 'unknown'; }
	}
}

class C extends B {
	public $foo {
		get { return $this->foo ?: 'unknown'; }
	}
}

$o = new C();
$o->foo = 1;
echo $o->foo;  /* echos 1 --> Calls C::__getfoo() 
			-> Calls B::__getFoo() 
			-> Calls C::__getFoo() which directly accesses $this->foo, previously set to 1 */
							
/*
Advantages:
  Won't have to muck with parent:: static junk

Disadvantage:
  - Limits flexibility of the developer as they can't directly access the
  	property without going through the parent, which may be a net advantage from an OO perspective, dunno.
  - Not what people would probably expect on how it works
*/