I'm using the 'Restrict Follower Selection' module (https://apps.odoo.com/apps/modules/11.0/mail_restrict_follower_selection/) to prevent unwanted partners showing up in 'Add followers' selection lists.

If have entered the value [('customer', '=', False)] and it is working properly, but I want to add a second value to prevent suppliers appearing in the 'Add followers' selection lists as well because I only want internal users in the company to be added as followers of documents.

What is the correct syntax for the value to achieve this?

Also, is there a good reference document available to learn more about how to construct these kinds of values for System Parameters and Record Rules?