Starts the upload process.
It works in the same way as if the Upload button was clicked.
Files are uploaded to the URL specified by the actionUrl property. If it is necessary to upload not just files, but some additional data, you can use the metadata properties. When upload completes, redirection to the redirectUrl occurs.
When Image Uploader uploads files, this method call is ignored (and the appropriate button is disabled). You should stop it first using the cancelUpload() method.