Negative / Exclusive-Or Visibility OR capability to use roles in visibility expressions

My main use-case for this is buttons, that are shown to people who have a specific set of roles:

Let’s say, you have two buttons, that each require a specific role + some check per role.

• Button 1: Role A, $currentObject/IsRead = false()
• Button 2: Role B, $currentObject/IsApproved = true()

Now some people have multiple user roles and thus can see both buttons, resulting in a lot of confusion over duplicate buttons. Currently you can not:

• Have both rules on one button, since you can not differentiate between the expressions for each user role
• Have only one button displayed, because the scope of visibility is local to the current element  

The only solution that currently works is, to use a visibility helper object, that checks all things to consider for visibility, and gives you a simple true-false flag for visibility.

I could think of multiple ways to solve this:

• Set rules when something should not be displayed.
• Use role inside the visibility expression
• Use some kind of exclusive display rule for elements