How to find the form handler?

Question

PHP

The site is on Bitrix, the form accepts data, processes it, sends everything ok. But where to find the handler?

<form class="form_modal form " method="POST" action="#" onsubmit="ym(<?= YMISUZU ?>, 'reachGoal', 'form_zakazat_zapchasti_isuzu_bokovaya'); return true;">

Pay no attention to ym. It's just not clear how to find the handler of such a form? If possible, in more detail (for those who know)

Answer 1

We open for ourselves such a thing Developer Tools in the browser.
We press F12, the Network tab, just in case, check the preserve log checkbox, submit our form and see what request went to the site

Answer 2

What is not clear? A string of data is sent to the same script that loaded the page. There, this string is "parsed" into parts and processed along with the form data.