Class Baz contains 1 abstract methods and must therefore be declared abstract (Baz::run)

Fails: "Fatal error: Class Baz contains 1 abstract methods and must
therefore be declared abstract (Baz::run)" (expected behaviour):

<?php
class Baz {
abstract function run();
}
?>

Works (no error message, is instantiable):

<?php
class Bar { }
class Foo extends Bar {
abstract function run();
}
?>

Is this correct? Why would this differ for inherited classes? And why
are these checks performed at runtime?

• Timm