Upload field allow users to choose file(s) they want to upload.
The filed uses Fineuploader: Multiple file upload plugin with image previews, drag and drop, progress bars. S3 and Azure support, image scaling, form support, chunking, resume, pause, and tons of other features.
array(
'id' => 'upload_1',
'type' => 'upload',
'title' => 'Upload',
'options' => array(
// 'attach' => true, // attach to post (only in metabox)
'filecount' => '101',
// 'allowed' => array( 'png', 'jpeg' ),
// 'delete-enabled' => false,
// 'delete-force-confirm' => true,
// 'retry-enable-auto' => true,
// 'retry-max-auto-attempts' => 3,
// 'retry-auto-attempt-delay' => 3,
// 'auto-upload' => false,
),
),