I don't get this one. Let's say you have this interface:

```php
interface Foo
{
  function bar($a);
}
```

Here is my implementation:

```php
class ConcreteFoo implements Foo
{
  function bar($a, $b = 'a')
  {
    // here, I've added $b
  }
}
```

Adding `$b` is what you reference as "adding a parameter to an implemented method "? If yes, `parameter` should be `argument` (at least, that's how I reference such variables everywhere in Symfony). But anyway, I fail to see how this is useful.