Refresh multiple-field attribute doc

Try to update the documentation about multiple-[field].

source/import_documentation/Mixins/widget-mixin.rst

@@ -125,19 +125,28 @@ Attributes
 
 ``multiple-[field]``
 ~~~~~~~~~~~~~~~~~~~~
+    This attribute allows to manage containers inside a resource.
     Show ``[field]`` as multiple field containing
     one widget for each child.
 
+    Multiple accepts a container's URL as value (= the ``field`` must refer to an URL) 
+    and creates an intern component to display it, its resource is this container.
+
     Multiple widget can be specified, example:
     ``multiple-skills="my-custom-multiple-widget"``. If argument is used
     without value, default multiple widget is used.
 
-    All attributes starting by ``each`` will be applied on each child, 
-    without the prefix ``each``.
 
-    - ``each-label-[field]``: label of each child of multiple widget
-    - ``each-class-[field]``: class of each child of multiple widget
-    - ``each-range-[field]``: range value of each child of multiple widget
+    It can be used in :
+
+    - Solid-display : the field in ``multiple-field`` will be transfered in a solid-multiple component by default.
+    If ``multiple-field`` is followed by something, this will be transfered inside a 
+    solid-display (``multiple-[field]-empty-widget``, ``multiple-[field]-next``) .
+    - Solid-form : the "field" in ``multiple-field`` will be transfered in a 
+    solid-form-multiple component by default. 
+    Thanks to the multiple attribute, it is possible to add and remove elements.
+
+    In both cases, the widget of ``multiple-[field]`` can be modified.
 
     For ``solid-form`` only: