[Form] Added doc for collection prototype

Author: marc.weistroff

book/forms.rst

@@ -917,6 +917,31 @@ the following inside ``ProductType``:
  ));
  }
 
+The collection type also give you the ability to embed a prototype of
+the collection form in your view. The prototype is a row of the collection
+without any data in it that serves as a template to add more items.
+To do so, you must set the ``prototype`` and ``allow_add`` options to ``true``.
+
+When your collection will be rendered, the html element containing your
+collection (div or table) will have a ``data-prototype`` attribute containing
+the rendered prototype, as a string. In order for you to display the
+prototype, you'll have to write a small JS to capture the attribute
+and insert it in the form. Here is a sample that you will have to adapt.
+
+.. code-block:: javascript
+ <script type="text/javascript">
+ jQuery('#add-element').click(function() {
+ var prototype = $('form#my_form #my_collection').attr('data-prototype');
+
+ // the level of the prototype is replaced by $$name$$
+ // you have to change this to the number of items + 1
+ prototype = prototype.replace(/\$\$name\$\$/g, '00');
+
+ // Append the prototype to the DOM
+ $('#my_prototype').append(prototype);
+ });
+ </script>
+
 .. index::
  single: Forms; Theming
  single: Forms; Customizing fields