In policy statements, the ARN is used in Principal and Resource elements.
arn:aws:s3:::bucket-name arn:aws:s3:::bucket-name/object_key
arn:aws:iam::account_id:root arn:aws:iam::account_id:user/user_name arn:aws:iam::account_id:group/group_name arn:aws:iam::account_id:federated-user/user_name arn:aws:iam::account_id:federated-group/group_name
The HTTP request body for the PUT Bucket policy operation must be encoded with charset=UTF-8.