How does the 'fx' queue in jquery auto start?

Question

I have read many answers and blog posts on the jQuery queues... and specifically this particular answer has helped a lot - https://stackoverflow.com/a/3314877/1315811 . But,

Answer 1

This bit of code within the queue code handles the auto-start:

if ( type === "fx" && queue[0] !== "inprogress" ) {
    jQuery.dequeue( this, type );
}

If the queue being queued is fx and the queue is not already in progress, dequeue is called.