Justpy Form: I want to know about on submit how the callback function works and how gets the form data

Question

I want to know how justpy pass the form data to the callback function. I want to debug that part.

I am using the QSelect component in my application. Here, the problem is that I am selecting multiple options but in the backend, it returns the first option selected value that is string of id. Now I want to check where it's converting a list to a string.

Thanks for your help!