public function append_modules_content( string $content ) : string {

		global $more, $post;
		$flexible_content = '';

		// Remove current filter to avoid recursive loop.
		remove_filter( 'the_content', [ $this, 'append_modules_content' ], $this->_the_content_priority );

		if ( $this->is_current_post_flexible( $post, $more ) ) {
			$flexible_content = $this->get_modules_content( $post );
		}

		// Re-add filter after parsing content.
		add_filter( 'the_content', [ $this, 'append_modules_content' ], $this->_the_content_priority, 1 );

		return $content . $flexible_content;
	}