[*] BO : Add block "override_form_extra" in list_header.tpl
{if !$simple_header}
<form method="post" action="{$action}" class="form">
{block name="override_form_extra"}{/block}
In AdminXxxxController, If we display list which are filtered by "variable" like
index.php?controller=AdminXxxx&variable=val&token=...
When using pagination or columns filters, the controller is called without our variable.
There are two methods to retrieve our variable: cookie or form Post.
To use the second opportunity, we need to put hidden input "variable" in the form.
So we need à block in the form to override.
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