public function isPublishable()
    {
        // No source
        if (!$this->CopyContentFrom() || !$this->CopyContentFrom()->ID) {
            return false;
        }

        // Unpublished source
        if (!Versioned::get_versionnumber_by_stage(
            SiteTree::class,
            'Live',
            $this->CopyContentFromID
        )) {
            return false;
        }

        // Default - publishable
        return true;
    }