You use JavaScript to configure the progressbar. Example: the progressbar_steps variable is used to indicate total number of Steps. If it's set to 50 as in this example, the progress bar will move like this: 2%, 4% 6% ... 100%, i.e. 50 steps.
The moveProgressBar() function is called whenever you want to move the progress bar. The argument to this function is how many steps you now want to move the bar. This argument is optional. If left out, the progress bar will simply move to the end.