Copy the whole div element which contains the text3 input element line and paste that block on a new line under itself.  Change text3 to text4 for the name and id.  You do not need a label for this field as it will be hidden soon so delete it.  Change the value to Gone.  Delete the readonly attribute.

Save and view in browser and you now have four input fields at the top of the form with one having no label and that one should contain Gone.  Change the type of the new one from text to hidden.  Try it again and the field should vanish.  However, it is still there.  Put something into the visible fields and press the submit button.  You should see the fields by name and the data in them (with Gone in the hidden field text4). 

This might seem useless but you can use hidden fields to send information in a form which the user never sees.  For example you could use JavaScript to find the resolution of the user's monitor and then put that into the hidden field to be sent with the other stuff.