[Form] Add new prototype_options

Author: michaelKaefer

reference/forms/types/collection.rst

@@ -303,6 +303,29 @@ type::
         ],
     ]);
 
+prototype_options
+~~~~~~~~~~~~~~~~~
+
+**type**: ``array`` **default**: ``[]``
+
+This is the array that's passed to the form type specified in the `entry_type`_
+option when creating its prototype. It allows to have different options depending
+on whether you are adding a new entry or editing an existing entry.
+
+    use Symfony\Component\Form\Extension\Core\Type\CollectionType;
+    use Symfony\Component\Form\Extension\Core\Type\TextType;
+    // ...
+
+    $builder->add('names', CollectionType::class, [
+        'entry_type'   => TextType::class,
+        'entry_options'  => [
+            'help'  => 'You can edit this name here.',
+        ],
+        'prototype_options'  => [
+            'help'  => 'You can enter a new name here.',
+        ],
+    ]);
+
 entry_type
 ~~~~~~~~~~