How display plugin modal in code

I have a general question. I know that flexicontent can be done easily.
But I would like to display a plugin
{modal url} text {/ modal} on the form in which I can only enter the php and html code.

JPluginHelper::importPlugin('system', 'modal');
$dispatcher = JEventDispatcher::getInstance();
$var1 = 'URL';
$var2 = 'text';
$results = $dispatcher->trigger('onAfterRender', array(&$var1, &$var2));
return ($results);

the result is text 'array'
Can you do it?

I guess you can compare it to item.php.
The question is not about flexicontent because flexi know how to do it.
This applies to the form in which I can add my php code. I retain the result by return.
Modal in html works ok. But I can not run the plugin inside the code.
Unfortunately, not all component authors have your knowledge.