Utilisation des filtres sur champs filtrable

yes !

I need also a permanent and hidden filter.
if I put it in URL it's only active if filter is activated and displayed.

Is there another possibility ?

Yes you can set it as a user session variable, and effect a specific category or effect when a menu item is active,

but i will need to check where to enter the code ...?

As I ask you in other posts, I manage a multisite with flexicontent.
I add some fields for site1, site2, .... with boolean values.

For the moment these values are manually selected in admin, but later I will try to make a plugin to put the values automatically with user rights.

For showing values in frontend I'd like to add always the filters hidden like site1=1 depending PHP value Server name.

So you want to set hidden forced filters depending on the domain used in the URL?

yes, completely! I use adv mod manager for displaying modules and menus dependant on domain name, and now I just have to filter content depending domain name in URL