Value List Based Automatic Permissions to Extend Permissions

Question

Curious if this is possible as I'm not able to get this working in the current configuration. I have a document class with the automatic permissions set to allow one user access with all rights: Carter Naff: Allow All 
 I have a property definition called Sub type with the following values and permissions: Sub Type A: default permissions 
 Sub Type B: Automatic Permissions - Johnny Cash - Read Only 
 
 I was hoping that when I select Sub Type B, that Carter Naff would have All Permissions and Johnny Cash would have Read Rights. This is not the case. The document class continues to only to allow Carter Naff. Although, I can see where automatic permissions applied the value list permissions but they seem to not be active. 
 
 I've not denied rights anywhere. 
 Thanks in advance!

Joonas Linkola · Answer

M-Files permission model only allows you to restrict permissions with additional permission settings, not extend them. Effective Permissions in the user guide has more details. 
 One possibility to give access rights to a specific document to additional individual users is to use a property such as "Additional contributors" on the document metadata and use that property on the class-level access control list. With this approach any users added to the "Additional contributors" property would get access to the document.