From manual page: https://php.net/class.recursivedirectoryiterator
The SplFileInfo Object has no isWriteable()-method:
$rdi = new RecursiveDirectoryIterator(DIR, FilesystemIterator::SKIP_DOTS);
$rit = new RecursiveIteratorIterator($rdi);
foreach ($rit as $fileinfo) {
//fileinfo is SplFileInfo-Object
echo $fileinfo . ":" . PHP_EOL;
$fileinfo->isDir(); // this method exists
$fileinfo->isReadable(); // this too
is_writeable($fileinfo); // this works
// error: PHP Fatal error:
//Uncaught Error: Call to undefined method SplFileInfo::isWriteable()
$fileinfo->isWriteable();
}