I've found another way to resolve my problem without creating a cb_field that I share with you :
With Joomla ACL : I create 3 groups and 3 access level with registered access (registered1, registered2, registered3)
CB LIST : I create 3 cb_list with 1 list with results for registered 1 , 1 list with results for registered 2, 1 list with results for registered 3 (all with level access : registered)
In my MENU, I have 3 items for LIST1 with level access registered1, LIST2 with level access registered2 and LIST3 with level access registered3
Then, every user have is own access level (registered 1 2 or 3)
In this way, user with level access 2, can only see MENU LIST2 and so access to LIST2
Hope one day I can do this with CB_Conditionnal
Frank
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