When generating documentation for a class which extends a built-in PHP class or implements a built-in PHP library, it would be nice to inherit the built-in documentation.

We currently do this for classes that are not built-in. For example, in the following example class B will inherit the documentation for the someMethod method from class A.

abstract class A {
  /*
   * Documentation goes here.
   */
  public function someMethod() {}
}

final class B extends A {
  public function someMethod() {}
}

Consider PhutilArray as another example. It would be nice if this class inherited documentation for the offsetExists method from http://php.net/manual/en/arrayaccess.offsetexists.php.