The signup form posts over AJAX and swaps itself for a thank you message about
700ms later. Nothing navigates. thankYouSelector is
#signup-thanks, so the MutationObserver is what notices.
The search box is here to prove it does not get counted.
Search ran, and no form_submit event was recorded — the
thank you message never appeared.
Submitted. The listener has the fields in hand and is waiting for
#signup-thanks to show up…
Note that none of these inputs have a name attribute. The keys
below come from each field's label text.
Try submitting the search box after the thank you message appears and you will get a second, bogus conversion carrying the search term. That is the trade-off of a purely element-based success signal — see the closing comments in the article for how to avoid it.