Adding private fields to an email form

Can one add invisible private fields to a finished email form (fields not visible to the form filler) and if so-How can you do this?

Creating a simple email form is easy but how can one insert invisible fields in the form for tracking and commenting?
This is an important feature for those who need to /rate/distinguish between/comment/etc on the data entries they collect without making the form filler aware of it.
This can be done in a form builder using the “Private Access Fields” option. In this option the form owner places the fields of his choice in a container element and defines it as “private access”. Once the form is saved and published the fields are not visible in the form, but are only accessible to the form owner in the data management tool.

Steps for using the access fields:
1) Enter the form’s report page.
2) Double Click on a specific entry line to enter the entry’s edit mode (or choose ‘Tools’>Edit).
3) Your access fields will now be sowing and you will be able to enter data in them.