Currently we have "Rating: A rating is an evaluation on a numeric scale, such as 1 to 5 stars."

Suggest amending to "an evaluation, commonly on a numeric scale", and creating a subtype EndorsementRating with definition "A positive rating that expresses a positive evaluation or endorsement."

Justification: some situations e.g. "pick of the week" critic's reviews, are implicitly positive. However if a numeric scale is not used, it is impossible to tell that the Rating should be taken as an endorsement.

We should also note that Rating is associated with some properties e.g. bestRating that assume a numeric scale ("The highest value allowed in this rating system. If bestRating is omitted, 5 is assumed."). We may need to soften this language to deal with non-numeric, non-scaled endorsement ratings (if necessary an unscaled endorsement can be seen as implicitly 5/5).

A related option would be for a Text-values of http://schema.org/ratingValue (e.g. "Critic's pick") to indicate a non-scalar system, in which case bestRating and worstRating would say "if bestRating is omitted and ratingValue is a number, 5 can be assumed."

Nearby: #780 for starRating discussion

/cc @gmackenz