<?php

function smarty_modifier_xml_string($string)
{
    $string = html_entity_decode($string, ENT_QUOTES, 'UTF-8');
    // beware of the order of search@replace values
    // str_replace() replaces left to right, it might replace a previously inserted value when doing multiple replacements
    $string = str_replace(['&', '<', '>'], ['&amp;', '&lt;', '&gt;'], $string);
    $string = preg_replace('/[^\x{0009}\x{000a}\x{000d}\x{0020}-\x{D7FF}\x{E000}-\x{FFFD}]+/u', ' ', $string);

    return $string;
}