// Simple validation (max file size 2MB and only two allowed mime types)
$validator = new FileUpload\Validator\Simple(1024 * 1024 * 2, ['image/png', 'image/jpg']);

// Alternatively, if you don't want to validate both size and type at the same time, you could use:
$mimeTypeValidator = new \FileUpload\Validator\MimeTypeValidator(["image/png", "image/jpeg"]);

// And/or (the 1st parameter is the max size while the 2nd is the min size):
$sizeValidator = new \FileUpload\Validator\SizeValidator("3M", "1M");

// Simple path resolver, where uploads will be put
$pathresolver = new FileUpload\PathResolver\Simple('/my/uploads/dir');

// The machine's filesystem
$filesystem = new FileUpload\FileSystem\Simple();

// FileUploader itself
$fileupload = new FileUpload\FileUpload($_FILES['files'], $_SERVER);

// Adding it all together. Note that you can use multiple validators or none at all
$fileupload->setPathResolver($pathresolver);
$fileupload->setFileSystem($filesystem);
$fileupload->addValidator($validator);

// Doing the deed
list($files, $headers) = $fileupload->processAll();

// Outputting it, for example like this
foreach($headers as $header => $value) {
  header($header . ': ' . $value);
}

echo json_encode(array('files' => $files));

$factory = new FileUploadFactory(new PathResolver\Simple('/my/uploads/dir'), new FileSystem\Simple(), array(
  new \FileUpload\Validator\MimeTypeValidator(["image/png", "image/jpeg"]),
  new \FileUpload\Validator\SizeValidator("3M", "1M") // etc
));

$instance = $factory->create($_FILES['files'], $_SERVER);

$fileupload->addCallback('completed', function(FileUpload\File $file) {
  // Whoosh!
});

$fileUploader->addCallback('beforeValidation', function (FileUpload\File $file
) {
  // About to validate the upload;
});

$fileUploader->addCallback('afterValidation', function (FileUpload\File $file
) {
  // Yay, we got only valid uploads
});