This question has been answered by sottwell. See the first response.
Hm. It's a hook. saveform, or some variation thereof. Looking for documentation on it. You can find the code in core/components/formit/elements/snippets/snippet.formitsaveform.php
Well, actually it's a snippet so you can find it in the Elements tree. Looks like it saves it to a JSON array.
Apparently based on the FormSave extra, so most of the properties should be portable. https://rtfm.modx.com/extras/revo/formsave
Try "FormitSaveForm" as the hook name. Should probably come before the email hook.