roundcubemail/program/lib/Roundcube/rcube_plugin.php
public function register_action($action, $callback)
    {
        $this->api->register_action($action, $this->ID, $callback, $this->mytask);
    }
public function register_action($action, $callback)
    {
        $this->api->register_action($action, $this->ID, $callback, $this->mytask);
    }
public function register_action ( $ action , $ callback ) { $ this -> api -> register_action ( $ action , $ this -> ID , $ callback , $ this -> mytask ) ; }
Register a handler for a specific client-request action

The callback will be executed upon a request like /?_task=mail&_action=plugin.myaction

@param string $action  Action name (should be unique)
@param mixed $callback Callback function as string
or array with object reference and method name
Register a handler for a specific client - request action