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LTI 1.3 LIS vocabulary for institution roles

LTI 1.3 LIS vocabulary for institution roles

According to the domain model, system roles are scoped to the user in the platform level, context roles are scoped to the user in the contexe level, but I can not find any information how institution roles are scoped. I would think that the most appropriate scope would be the tool deployment level. This would allow to manage fine grained access control. Is there any best practice?