Василий Наумкин

<div id="connect_table">
	[[!resource?tpl=`myForm`]]
</div>

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    extract($_POST);
}
$count = $count1 + $count2 + $count3;

return $modx->getChunk($tpl, array(
	'count' => $count
));

<form action="[[~[[*id]]]]" method="post" class="form_db">
	<input type="number" name="count1" value="5" />
	<input type="number" name="count2" value="7" />
	<input type="number" name="count3" value="2" />
	<button type="submit" name="submit">ok</button>
</form>
<p>[[+count]]</p>

if ($modx->event->name == 'OnHandleRequest') {
	if (!empty($_REQUEST['action']) && $_REQUEST['action'] == 'send_text') {
		// Можно работать
	}
}

http://sitename.ru/?action=send_text

$modx->runSnippet('mySnippet', $myParams);