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With Rating being a type, it should be possible to format look up and formula into a directly into Rating.
Right now this is not possible, without the use of Automation even so a rating is a disguised Number.
Adding this functionnaly would help application
that have to deal with things like community ratings.
Because a Rating is Number between 0 and a max rating, the resulting value in a formula should be clamp with 0 as the min and the max rating as the max.