//---
		// load_module() will load a module into the framework
		// @param object $module_object
		//---
		function load_module( &$module_object ) {			
			if ( !is_object( $module_object ) ) {
				return false;
			}
			$module_name = $module_object->identitfier;
			$this->modules[ $module_name ] = &$module_object;			
		}
		
		//---
		// trigger_event() will trigger an event to all loaded modules or selected modules
		// @param string $event
		// @param mixed $module
		//---
		function trigger_event( $event, $module='' ) {
			if ( empty( $module ) ) {
				// trigger event to all loaded modules
				foreach( $this->modules as $name=>$object ) {
					if ( method_exists( $object, $event ) ) {
						return $this->modules[ $name ]->$event();
					}
				}
			} else if ( is_array( $module ) ) {
				// trigger event to a selected number of modules
				foreach( $this->modules as $name=>$object ) {
					if ( in_array( $name, $module ) && method_exists( $object, $event ) ) {
						return $this->modules[ $name ]->$event():
					}
				}
			} else {
				// trigger to single module
				if ( method_exists( $this->modules[ $name ], $event ) ) {
					return $this->modules[ $name ]->$event();
				}
			}
		}