[Form] Added explicit getParent() call in types inheritance mechanism

form/create_custom_field_type.rst

@@ -67,14 +67,31 @@ check out the `ChoiceType`_ class.
     extend from ``AbstractType`` is only a convenience way of implementing the
     required ``FormTypeInterface``.
 
-There are three methods that are particularly important:
+There are a few methods that are particularly important:
 
 .. _form-type-methods-explanation:
 
+``getParent()``
+    This return the class name of the type configuring the form before. It
+    means all the other methods below will be called with this parent type
+    and all its type extensions before calling the ones defined in your
+    custom type.
+    By default, all classes inherit the ``AbstractType::getParent()`` which
+    defines the ``FormType`` as parent type to re-use its options and
+    configuration.
+
+``configureOptions()``
+    This defines options for your type that
+    can be used in ``buildForm()`` and ``buildView()``. Options are inherited
+    from parent types and parent types extension but you can create any custom
+    option you need.
+
 ``buildForm()``
     Each field type has a ``buildForm()`` method, which is where
-    you configure and build any field(s). Notice that this is the same method
-    you use to setup *your* forms, and it works the same here.
+    you configure and build any field(s) depending on options defined in
+    ``configureOptions()``.
+    Notice that this is the same method you use to set up *your* forms, and it
+    works the same here.
 
 ``buildView()``
     This method is used to set any extra variables you'll
@@ -83,18 +100,14 @@ There are three methods that are particularly important:
     set) the ``multiple`` attribute on the ``select`` field. See
     `Creating a Template for the Field`_ for more details.
 
-``configureOptions()``
-    This defines options for your form type that
-    can be used in ``buildForm()`` and ``buildView()``. There are a lot of
-    options common to all fields (see :doc:`/reference/forms/types/form`),
-    but you can create any others that you need here.
+``finishView``
+    Same as ``buildView`` but to configure the nested field views.
+    This method as no use with types that build compound forms.
 
 .. tip::
 
-    If you're creating a field that consists of many fields, then be sure
-    to set your "parent" type as ``form`` or something that extends ``form``.
-    Also, if you need to modify the "view" of any of your child types from
-    your parent type, use the ``finishView()`` method.
+    If you're creating a field that consists of nested fields, then be sure to
+    set the parent type as ``FormType::class`` or one of its child.
 
 The goal of this field was to extend the choice type to enable selection of the
 shipping type. This is achieved by fixing the ``choices`` to a list of available