Станислав

<?php
$old_price = str_replace(' ','',$old_price);
$price = str_replace(' ','',$price);
$diff = $old_price - $price;
$output = $diff / $old_price * 100;
$output = round($output);
return $output;

<span class="sale">{'sale' | snippet : ['price' => $price, 'old_price' => $old_price]} %</span>

{$_pls['vendor.name']}

[[+vendor.name]]

$result = $modx->runSnippet('Register', $scriptProperties);