docs: public final boolean isAssignableFrom (@Nonnull final AbstractJSClass aDerived)
    {
      ValueEnforcer.notNull (aDerived, "Derived");
  
      // to avoid the confusion, always use "this" explicitly in this method.
      if (this == aDerived)
        return true;
  
      final AbstractJSClass b = aDerived._extends ();
      if (b != null && isAssignableFrom (b))
        return true;
  
      return false;
    }