htmlentities() replacement that converts all entities in a string into character entities (suitable for XML documents)

xmlentities.php

<?php 
/**
 * Works like htmlentities() but only encodes entities as numeric codes
 * instead of names (for use in XML).
 */
function xmlentities($str, $encoding = 'UTF-8', $asList = false)
{
    $list = array();
    $ent = '';
    $chars = preg_split('//u', $str, -1, PREG_SPLIT_NO_EMPTY);
    foreach ($chars as $chr) {
        // FYI: 'UCS-4BE' encodes all characters as a 4 byte 32bit int
        $str = mb_convert_encoding($chr, 'UCS-4BE', $encoding);
        $len = mb_strlen($str, 'UCS-4BE');
        for ($i = 0; $i < $len; $i++){
            $s = mb_substr($str, $i, 1, 'UCS-4BE');
            list(, $val) = unpack('N', $s);
            if ($val < 128) {
                $list[] = chr($val);
                $ent .= htmlspecialchars(chr($val), ENT_QUOTES, $encoding);
            } else {
                $list[] = $val;
                $ent .= '&#' . $val . ';';
            }
        }
    }
    return $asList ? $list : $ent;
}