Example of TOC code

/**
     * Create Content_TOC:
     * 1) Setup default header elements
     * 2) Register shortcode
     */
    protected function __construct() {
        // Register TOC shortcode
        add_shortcode( 'hm_content_toc', array( $this, 'shortcode' ) );
        // Shortcake UI plugin integration (Source: https://github.com/fusioneng/Shortcake)
        if ( function_exists( 'shortcode_ui_register_for_shortcode' ) ) {
            add_action( 'init', array( $this, 'register_shortcake_ui' ) );
        }
    }