code: 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;
    }
docs: Checks the relationship between two classes.
  <p>
  This method works in the same way as {@link Class#isAssignableFrom(Class)}
  works. For example
  <code>baseClass.isAssignableFrom(derivedClass)==true</code>.
  
  @param aDerived
  class to check
  @return <code>true</code> if this class is assignable from the passed class