- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
// your code goes here
$test = "moind3re pro_blème";
var_dump(preg_match("/^[a-zA-Z\x{00C0}-\x{017F}]/u", $test));
//var_dump (filter_var($test, FILTER_SANITIZE_SPECIAL_CHARS, FILTER_FLAG_STRIP_LOW));