minor #16664 [Form] Add new prototype_options (michaelKaefer)

This PR was submitted for the 6.0 branch but it was merged into the 6.1 branch instead.

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[Form] Add new prototype_options

Related PR: symfony/symfony#45605

Commits
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ec76b6a [Form] Add new prototype_options

Author: javiereguiluz

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
 ~~~~~~~~~~