/**
  * Returns the instance of the plugin.
  *
  * @return TM_Extra_Product_Options.
  */
 public static function instance()
 {
     if (is_null(self::$_instance)) {
         self::$_instance = new self();
     }
     return self::$_instance;
 }
 /**
  * Load main plugin interface
  */
 function TM_EPO()
 {
     return TM_Extra_Product_Options::instance();
 }