Description:
------------
On an inherited methods that uses parameter type hints it is not possible to specialize a type hint. By "specialize" I mean that the type hint on the inheriting class's method is able to type check an inherited class of the previous type hint.

I have found several cases, where this behaviour would be extemely useful. The Specification Pattern poses a good example.

Certainly you can work around it by not using type hints and do some "instanceof" or "get_class()" checking inside, throwing an exception in unwanted cases. It would however be nice if the language itself could support such a behaviour.

Reproduce code:
---------------
<?php

interface ISpecification {
    
    public static function isSpecifiedBy($object);
    
}

class FooSpecification implements ISpecification {

    public  static function isSpecifiedBy($object) {
        echo get_class($object);
    }

}

class BarSpecification implements ISpecification {

    public static function isSpecifiedBy($object) {
        echo get_class($object);
    }

}

class Foo { }

class Bar extends Foo { }

FooSpecification::isSpecifiedBy(new Foo());
BarSpecification::isSpecifiedBy(new Bar());

?>

Expected result:
----------------
For this not to throw a compile time error

Actual result:
--------------
Fatal error: Access level to FooSpecification::isSpecifiedBy() must be public (as in class ISpecification) in [...] on line 9