Modal plugin in calc element

[tadzio]

I would like to put a modal plug-in on the form.
In Calculation window like this:
JPluginHelper::importPlugin('system', 'System - Regular Labs - Modals');
$dispatcher = JEventDispatcher::getInstance();
$results = $dispatcher->trigger('onMyFunction', array(&$var1, &$var2));
return ($results);

But
I do not know what is it onMyFunction
$var1 = 'myURL' ?