no submit_button in documentation?

[RobinManoli]

It seems to me that the submit_button is mandatory, yet it is not written in the examples. Besides, one might not even want to submit the form by a submit button, but trigger it differently (through onchange for example)

[jfeldstein]

An explicit submit button is optional.

If you don't specify a manual submit button, it'll automatically submit whenever the file selector changes. If you do set a manual submit button, the plugin will bind clicks on that element to starting the upload.