title: How do you add UI inside cells in a google spreadsheet using app script?
body: <p>I'd like to add buttons to specific cells in Google docs spreadsheet.  The <a href="http://code.google.com/googleapps/appsscript/guide_user_interfaces.html#ViewUIElements">apps script UI documentation</a>  talks about how to add a new panel, but it's not clear how UI in that panel could be attached to specific rows or cells.</p>
  
  <p>Is it possible to add UI to particular cells, or are we limited to adding new panels?</p>