public function startsWith($substring, $caseSensitive = true)
{
$substringLength = \mb_strlen($substring, $this->encoding);
$startOfStr = \mb_substr($this->str, 0, $substringLength, $this->encoding);
if (!$caseSensitive) {
$substring = \mb_strtolower($substring, $this->encoding);
$startOfStr = \mb_strtolower($startOfStr, $this->encoding);
}
return (string) $substring === $startOfStr;
}