title: Is there an event to capture the Submit button's press event in a Google form/survey?
body: <p>I have a Google form with some fields like Email Address, Name, etc.   What I'd like to have happen is this:</p>
  
  <ol>
  <li>User presses "Submit" after they've filled in the fields.</li>
  <li>I look at what is in the Email Address field to check if it exists in a column from a spreadsheet.</li>
  <li>If the Email Address doesn't exist, I append it to that column to maintain a list of unique (by email) registrants.</li>
  </ol>
  
  <p>Figured that it would mean overriding a Submit-related event, adding in my logic for checking some cells, and then writing to the (last cell + 1), but I can't seem to find anything for the event of that button.  Instead, <strong>all the submission event questions/search results I've seen are about making a new form and submit button from scratch</strong>.  To reiterate: I can't find anything about the <em>default</em> Google form/survey's Submit button and hope to avoid manually adding a submit button since that default one is already provided.</p>
  
  <p>Is there a way to detect that default Submit button's press for a default Google form/survey?  If so, what's the name of that event and can I override it?</p>