A from engagement event is being fired whenever the user interacts with any form field by changing its value. This can for example mean entering text into an input element or into a text area, selecting a radio option or choosing any number of options from a dropdown ( in this case, if the time between choosing 2 options does not exceed a time limit then only 1 event is submitted with the updated values to avoid too many hits to the server and for more comprehensive data ).

Parameters

form_identifier: a unique string that is generated to individually identify each form accross pages.
form_step_number: a numeric index that shows which form step is the current one. (ex. 2 means that the current is the 2nd field within the form) Please note that a set of radio buttons or a dropdown with multiple options that can be selected count as 1 field.
form_field_type: one of the following: multi select checkbox, color selector, date selector, date-time-local selector, email input field, file input field, image input field, month input field, number input field, password input field, radio / single value input field, range input field, search input field, free text input field, time input field, url input field, week input field.
form_field_name: the name HTML attribute of the given form field. Often times the same name that is visible after form submission (ex: first name)
form_field_entry_count: the count of how many times the user has interacted with the given form field within the current workflow. (ex 2 means that the user has already entered the value and then came back to update it).
form_field_id: the id HTML attribute of the given field that is also visible in the website code.
form_filed_value: the value that has been selected by the user. You can only get data on fields where you can choose from a number of options (ex dates, time, color, dorpdowns etc). For fields that accept free text, password or email you will see “value hidden” to avoid tracking Personally Identifiable Information.

Utilization

You can use this event in quite some ways. You can investigate which form fields may be problematic by inspecting high values for form_field_entry_count. You can track form progression by inspecting which are the highest form_step_numbers for a given form. You can create remarketing or analytics audiencies of users who select from a certain set of options that you are interested in.